Hard vs. Soft ND grads on Cropped sensor

[HoppyUK]

I'm just not seeing focal length anywhere in the equation Jim. I stick a grad on 24mm lens or a 135mm lens and I still have a range from 0EV to the maximum density of the filter. The reasoning I'm seeing from other people would seem to infer that a wider lens uses more of the grad and it just doesn't.

The light passing through the filter will affect the image circle (about 45mm diameter for Canon EF lenses) and that circle is the same size whatever the focal length of the lens producing it.

Bob

It does Bob Put a piece of cling film over a UV filter and mark it with a permanent pen. Try it on different lenses, or a zoom, and see how many of the marks are visible (stop down to make them clearer).

For the same reason, if you use a grad on a super-wide, the corners are darker because the lens looks through the edges of the filter at an angle, making the filter effectively thicker and therefore more dense. This effect is particularly noticeable when using a ten-stop ND - corners can be two or three stops down on the centre.

With a longer lens, it only sees a small area of the filter in the middle where the amount of gradation is very slight, made even less by the reduced depth of field throwing it further out of focus.

Edit: but it's not focal length directly, it's field of view.

 

[Canon Bob]

It does Bob Put a piece of cling film over a UV filter and mark it with a permanent pen. Try it on different lenses, or a zoom, and see how many of the marks are visible (stop down to make them clearer).

One for tomorrow Richard....it's French bedtime here now.
I'll make a 72mm cling film filter with concentric circles of different colours (felt pens) and then shoot a white wall with the 50L on my 30D and then the 85L on a 1Ds3 and you reckon I'll see identical patterns.

Bob
PS....I'll get Mrs CB to make a conical hat with a "D" emblazoned on it just in case

 

[odd jim]

One for tomorrow Richard....it's French bedtime here now.
I'll make a 72mm cling film filter with concentric circles of different colours (felt pens) and then shoot a white wall with the 50L on my 30D and then the 85L on a 1Ds3 and you reckon I'll see identical patterns.

Bob
PS....I'll get Mrs CB to make a conical hat with a "D" emblazoned on it just in case

Yes, you will see identical patterns and that's my point entirely! The sensor makes no difference but the fov of the lens does, the fact you expect to get identical results with different sensors suggests you agree with what I'm saying and that the fov of a lens makes the difference??!

Back to what I said about identical results and behaviour of an ND on a crop sensor through 10mm and an FF sensor through 16mm.

 

[Canon Bob]

.... the fact you expect to get identical results with different sensors suggests you agree with what I'm saying and that the fov of a lens makes the difference??!

I don't expect identical results Jim, I was restating Richards ascertion. (Although I'm starting to get less certain that I will see a difference).

Bob

 

[ShutterWork]

Blimey...blimey....blimey!!!

Someone's gonna have to write an idiots guide for me on this when it's all clear..

 

[HoppyUK]

One for tomorrow Richard....it's French bedtime here now.
I'll make a 72mm cling film filter with concentric circles of different colours (felt pens) and then shoot a white wall with the 50L on my 30D and then the 85L on a 1Ds3 and you reckon I'll see identical patterns.

Bob
PS....I'll get Mrs CB to make a conical hat with a "D" emblazoned on it just in case

Hold on with the hat Bob! Maybe Mrs CB could make me a humble pie instead... Or a small one perhaps. I'm not quite sure what it is you're driving at here, but for my part it's not quite so clear-cut as I suggested earlier.

Sorry, this is getting technical. It may not be quite as straightfoward as simple field of view. I've just done my own test mentioned above, with blobs of felt tip on the cling film and filter, and popped it on my 24-105L - which I've not done previously, only on the 17-40L which is what I always use for grads.

To my astonishment, when you zoom the lens, the blobs don't move. They quickly get more and more out of focus as focal length increases, which amounts to much the same thing in practice so this is somewhat moot, but they hardly move at all.

Somewhat puzzled, I put the filter/blobs on the 17-40L - and normal service was resumed. Zoom the lens, and the number of blobs visible reduces with focal length increasing.

For comparison, with the 24-105L I can see about five blobs across the frame and that remains constant as you zoom. With the 17-40L, I can see six at 17mm, reducing to three at 40mm.

It then occured to me that if I set the 24-105L at 40mm, I should get a darker grad effect than with the 17-40L at 40mm (everything else the same) and that's exactly what I got. Nothing dramatic, but certainly there.

I'm concluding therefore that the area of the filter seen by the lens, and therefore the extent of the grad effect, is not strictly determined by focal length and field of view in the scene alone - though they appear to be the dominant factors. It also depends on the distance the filter is from the entrance pupil which is a known moveable feast on many zooms.

I've noticed this before with these two lenses, when fiddling about with a nodal rail for stitched panoramas. To get things to line up exactly with close range objects, the lens must pivot around the extrance pupil and I noticed that with the 24-105L it didn't change much as you zoom, whereas with the 17-40L it did (slightly).

So, taking all this on board, it's quite possible to get slightly different grad results with lenses of the same focal length and field of view on the same camera (as I've proved) and that when focal lengths are equalised in terms of field of view with differerent formats, the results could change again, according to individual lens design. I would also expect there to be far less variables of this nature with primes than zooms.

Phew! Apologies for the long post, and for the confusion earlier. With creme anglaise please Bob

 

[HoppyUK]

Blimey...blimey....blimey!!!

Someone's gonna have to write an idiots guide for me on this when it's all clear..

Sorry Anand

If it was me, and I had to choose just one, I'd get a Lee three stops (0.9) hard grad. That will give you some great results Or if that's unavailable, a two stops (0.6) hard HiTech, or maybe a HiTech three stops soft cut.

See how you get on, and build from there. You'll need two or three at least to cover everything just the way you want, but that's largely down to personal taste.

 

[ShutterWork]

Sorry Anand

If it was me, and I had to choose just one, I'd get a Lee three stops (0.9) hard grad. That will give you some great results Or if that's unavailable, a two stops (0.6) hard HiTech, or maybe a HiTech three stops soft cut.

See how you get on, and build from there. You'll need two or three at least to cover everything just the way you want, but that's largely down to personal taste.

Thanks Richard, will research these further and buy. Also will read your long post with a fresh mind tmrw..kind of get the gist. Cheers for all that hard work. Much appreciated

 

[dinners]

Great thread folks - very informative.

On a lighter note - the cling film and felt pens - I'd have loved to have seen some shots of the the testing taking place..

 

[EdBray]

We might need more than one humble pie cooking.

When you try it Bob, can you also use the 16-35L on the 1D3 and the 24-70L on the 1Ds3 that way you should be able to equalise the field of view, or with primes the 100L on the 1D3 and the 135L on the 1Ds3, although after reading Richard's efforts anything could be the end result.

One for tomorrow Richard....it's French bedtime here now.
I'll make a 72mm cling film filter with concentric circles of different colours (felt pens) and then shoot a white wall with the 50L on my 30D and then the 85L on a 1Ds3 and you reckon I'll see identical patterns.

Bob
PS....I'll get Mrs CB to make a conical hat with a "D" emblazoned on it just in case

 

[Moreorless]

The effect of distance and F number was mentioned before but are those going to relate to FF and Crop?

 

[Canon Bob]

We might need more than one humble pie cooking.

When you try it Bob, can you also use the 16-35L on the 1D3 and the 24-70L on the 1Ds3 that way you should be able to equalise the field of view, or with primes the 100L on the 1D3 and the 135L on the 1Ds3, although after reading Richard's efforts anything could be the end result.

You must think I'm weighed down with gear Eddie I haven't got a 16-35, 24-70 or 1D3 (instead, 17-35, 28-70 and 1D4)
I'm going primes for this but have to go shopping first for felt pens and a couple of tins of stewed humbles for the pies.

Bob

 

[Canon Bob]

Some initial tests and conclusions......surprising and not so surprising.

I coloured up a plain filter with alternating concentric circles of red and green. Sticking the filter on my 85/1.2 on a FF body showed more rings than when used on the 50/1.2 on a crop body.
I then went back to the FF but paired up with the 50/1.2 and saw fewer rings than the 85/1.2 showed
Here's the bit that surprised me (although maybe it shouldn't have), if I put the 85/1.2 on the FF body and stop down the aperture whilst holding the DoF preview button then the rings slowly spread out and disappear out of sight at the edges.

Ititial conclusions are;
Sensor size does make a difference how much of the filter gradient gets used.
Smaller apertures use less of the filter.
The diameter of the front element affects the amount of used filter ***

*** The 85/1.2 has a narrower AOV but a larger diameter front element and sees more of filter area at equal aperture values.

So how does an EF-S lens behave?

Bob

 

[HoppyUK]

Good stuff Bob

Clearly things are not entirely predictable and not simply related directly to focal length and field of view comparisons, even if that may be the dominant factor. A crop vs full frame comparison would be interesting, with EF-S and EF lenses, field of view equalised.

I've thought of an easier way of doing it, with a clear plastic ruler BluTacked across the front of the lens. At f/16 you can just about see the markings.

I would post some comparison pics up but I'm prettty busy over the next couple of days, and they would only illustrate what I've said earlier. As a comment, I think the main relevance is with wide angles because whichever way you odds it grads are pretty useless on longer focal lengths.

 

[odd jim]

Interesting... Is there anyone out there (lucky enough!) that can test the EFS 10-22 on crop vs the 16-35 in FF?

 

[ShutterWork]

Having read this more carefully and with a fresh mind, it does seem to make sense to me now...Brilliant brilliant information on this thread...!!Cheers to Bob and Richard for their efforts with the practical tests...sure most of us do appreciate on this.

Apologies though, didn't expect my question to cause so much trouble and debate...

Kind of made up my mind to go with Lee 0.9 hard gard, hope it's still available?? Thank you all for the efforts.

 

[Canon Bob]

I think that the hard grad is the right choice Anand although it was only the discussion in this thread (and the testing) that showed me that the obvious isn't always as obvious as it seems.

Bob

 

[ShutterWork]

I think that the hard grad is the right choice Anand although it was only the discussion in this thread (and the testing) that showed me that the obvious isn't always as obvious as it seems.

Bob

Thanks Bob....great effort

 

[AndyB1976]

I'm prepared to don the pointed D Hat now but need to ask...

Would an internal focus/zoom effect your results differently than an extending barrel on the same sensor at the equivalent focal lengths?

Can you use the results from here, with what we shall call a 'fixed grad' blobs/circles and apply that in the field where you would normally slide the grad according to composition? In other words is the test entirely relevant to in the field conditions?

Sorry if its buried in those preceding answers, I couldn't quite correlate them

 

[HoppyUK]

I'm prepared to don the pointed D Hat now but need to ask...

Would an internal focus/zoom effect your results differently than an extending barrel on the same sensor at the equivalent focal lengths?

Can you use the results from here, with what we shall call a 'fixed grad' blobs/circles and apply that in the field where you would normally slide the grad according to composition? In other words is the test entirely relevant to in the field conditions?

Sorry if its buried in those preceding answers, I couldn't quite correlate them

On the evidence of my filter/blobs test, I think the answer is probably yes. That's only a guess, but it's the most obvious difference between the two lenses I tried, 17-40L and 24-105L, when used at the same focal lengths. And hence why I suspect primes of the same focal length would probably be the same, or extremely similar, because the optical designs will be similar.

But while I find this stuff quite interesting, the differences were not massive and it is still very substantially true that focal length and especially field of view that is the main determining factor in how much of the filter the lens sees and therefore the strength of the grad line.

Different lenses may vary a bit according to individual design, but the fact remains that you get a stronger grad effect with wide angles, and the wider the stronger, and with longer lenses of quite modest focal length like 80-100mm, the grad effect fades to virtual invisibility. So even after all that, it's kinda moot

For practical purposes, there are lots of variables (as discussed previously) and you should do your own tests with different focal lengths and also with different f/numbers - there's a marked difference between say f/4 and f/16 on the strength of the grad line.

 

[AndyB1976]

Thanks for that Richard!

It had been an interesting thread for something I hadn't even considered before and good input from all contributors.

cheers


Andy

 

[EdBray]

So am I cooking pie or not?

 

[specialman]

Interesting thread....

Wonder when WEX will start selling blu-tak, marker pen and clingfilm filter sets... They seem quite popular on TP at the moment

 

[Canon Bob]

So am I cooking pie or not?

I'd certainly get the custard warming Eddie and then be prepared to cut the pie into several large slices. Don't bother setting a place for me though....I'll be still be full after eating my hat.

Bob

 

[ShutterWork]

Managed to get Lee 0.9 hard cut and standard NDs. Readily avail in stock @ Teamwork ..test time soon..thank you all in helping me choose my gear.

 

[odd jim]

I like pie...