My filters consistently decrease my negative contrast - what am I doing wrong?

pentaxuser · Apr 25, 2018

dante said:
Dark orange and red filters tend to induce backfocus at the film plane with a lot of non-APO lenses, and CCD AF sensors and rangefinders aren't really equipped to compensate for this (the CCD performance is also degraded by the huge amount of light cut by the filter). APO lenses have red corrected to the same focusing plane as green and blue, so it's not so bad. And stopped down, it's often eliminated by DOF.

Are most modern SLR lenses APOs and which cameras have CCD AF sensors? I had always thought that CCD was peculiar to digital cameras. I ask this because I use orange and red regularly on my Pentax AF lenses on a MZ7 and have never seen this problem with AF focus.

This has really got me confused. If anyone else cares to help clear up this problem with red and orange filters, APO lenses and CCD sensors please feel free to contribute. Would the same focus problem occur with say a green filters also as it has as much light reducing power as certainly orange and almost as much as red. Presumably ND filters will create the same AF problem as well?

Thanks

pentaxuser

Sirius Glass · Apr 25, 2018

dante said:
Dark orange and red filters tend to induce backfocus at the film plane with a lot of non-APO lenses, and CCD AF sensors and rangefinders aren't really equipped to compensate for this (the CCD performance is also degraded by the huge amount of light cut by the filter). APO lenses have red corrected to the same focusing plane as green and blue, so it's not so bad. And stopped down, it's often eliminated by DOF.

I have never had that happen with any slr camera ever. I have used those filters with many cameras. Of course I am talking about film cameras.

Billy Axeman · Apr 26, 2018

Only very courageous people are using filters.

pentaxuser · Apr 26, 2018

Sirius Glass said:
I have never had that happen with any slr camera ever. I have used those filters with many cameras. Of course I am talking about film cameras.

Nice to know there are others who have not experienced the problem either. As I said it is complete news to me that red and orange give AF problems. As far as I am aware I don't think I have ever seen it mentioned in any book on analogue photography and not until the posts from dante can I recall it ever being said on Photrio

My knowledge of things digital and scanning is zero but from your last sentence I think you are saying that film cameras do not have CCDs If that's the case I wonder why CCDs were mentioned in the context of filters on the analogue section?

pentaxuser

neilt3 · Apr 26, 2018

pentaxuser said:
Nice to know there are others who have not experienced the problem either. As I said it is complete news to me that red and orange give AF problems. As far as I am aware I don't think I have ever seen it mentioned in any book on analogue photography and not until the posts from dante can I recall it ever being said on Photrio

My knowledge of things digital and scanning is zero but from your last sentence I think you are saying that film cameras do not have CCDs If that's the case I wonder why CCDs were mentioned in the context of filters on the analogue section?

pentaxuser

CCD's are used in the Auto-Focus module in SLR's and DSLR's in the bottom of the mirror box where some of the light is redirected down via secondary mirror .
IIRC a pair is required for each A/F sensor point , so in Minolta's first 7000AF autofocus camera from 1985 with just the one central A/F point , 1 pair would have been used .
Modern cameras use a lot more .
Nothing to do with how the image is recorded , as in film or digital , in this context or subject .

Regarding A/F and filters , I've never had a problem with A/F acuracy focussing through the filter .
Even with an R72 ( infrared only pass ) filter , my Minolta Dynax 9 has no problem focussing .
On a bright day , you can hardly see past it , so I mount a rangefider cameras turret viewfinder for composition in the hotshoe and leave the central A/F point take care of the auto-focus . .
The camera also happily meters correctly through it too .

The cameras are focussing the light that reaches the film , so seems to work fine .
I've not had any problems using other A/F cameras with filters either .

Billy Axeman · Apr 26, 2018

To prove the inevitable, I have done a quick test with a Nikon F6, AF Nikkor 35mm f/2.0 D, and three Nikon filters: red (R60), green (X1), and blue (B12) in low light conditions and auto-focus works without a single hitch.

pentaxuser · Apr 26, 2018

Billy Axeman said:
To prove the inevitable, I have done a quick test with a Nikon F6, AF Nikkor 35mm f/2.0 D, and three Nikon filters: red (R60), green (X1), and blue (B12) in low light conditions and auto-focus works without a single hitch.

We seem to have lost dante, the author of the problems with AF and red and orange filters and CCD I asked him what I thought were perfectly reasonable questions on these matters and given his striking announcement which seems to be taking others here by surprise I had expected to hear about the source of his information.

I do hope he replies. Maybe it is just me but on Photrio i had expected that when someone asserts things that constitutes startling news then at least he shares that information with us and can answer perfectly reasonable questions on it.

pentaxuser

Sirius Glass · Apr 26, 2018

pentaxuser said:
We seem to have lost dante, the author of the problems with AF and red and orange filters and CCD I asked him what I thought were perfectly reasonable questions on these matters and given his striking announcement which seems to be taking others here by surprise I had expected to hear about the source of his information.

I do hope he replies. Maybe it is just me but on Photrio i had expected that when someone asserts things that constitutes startling news then at least he shares that information with us and can answer perfectly reasonable questions on it.

pentaxuser

Yep

Billy Axeman · Apr 27, 2018

This reminds me of discussions on digital forums where people are running in endless circles why their auto-focus doesn't work in certain conditions, why it is so slow, and the advantages and disadvantages of certain systems.

Personally I find the original question from the OP more interesting: is there perhaps a flaw in Cokin's system in which the filter is exposed to light from all sides with less contrast as a result. I saw that Cokin has also a hood, but it is very short so perhaps it is actually adapted to short lenses to make it more or less universal (hence my idea to use a bellows shade from Hasselblad).

neilt3 · Apr 27, 2018

The Colin hoods are a modular hood .
Wide angle lenses might need just one section , a telephoto lens might use five clipped together .
I also have a bellows type lens shade that they made that slots into the holder .
I don't know if they still make these , I have one for the P size but have been unable to find one for my Z-pro size .

I've been using the Cokin and Hitech filters for years and never had a problem .
Part if the side and all of the top and bottom of the filter is exposed to light when used in the correct holder and there is no problem .
If an ND grad is in the holder on the furthest away from the lens slot , care should be taken to shield excess light from entering .
A darker filter held by hand in front of the lens might be allowing excess light past causing reflection and flair on the filter surface , reducing contrast .

Billy Axeman · Apr 27, 2018

Thanks neilt3, I didn't know they they were stackable (I only saw one in a price list). If you have a 3D printer another solution could be to make a clip-on hood with an extra overlap on the filter side to cover the edges.

DREW WILEY · Apr 27, 2018

Strange encountering a bunch of autofocus and DLSR meter debate on a large format thread. After I focus the view camera, I always recheck focus if a strong filter is involved. Lenses differ, and so in fact do the modes of internal metering in small cameras. Generalities just don't make the grade.

neilt3 · Apr 27, 2018

DREW WILEY said:
Strange encountering a bunch of autofocus and DLSR meter debate on a large format thread. After I focus the view camera, I always recheck focus if a strong filter is involved. Lenses differ, and so in fact do the modes of internal metering in small cameras. Generalities just don't make the grade.

Not that strange , have you never heard of anyone using a 35mm SLR or DSLR to take a meter reading for another format ( medium or large format) if they haven't a hand held meter ?

I tend to use my Minolta Spotmeter for such as this , but I have used camera to take a reading in the past if I didn't have the meter with me .
Also not everyone can afford a Spotmeter but have a 35mm ( or what-ever) camera that can be utalised with good results .

Much better than what you get from an APP on a Smartphone as far as I'm concerened .

neilt3 · Apr 27, 2018

Billy Axeman said:
Thanks neilt3, I didn't know they they were stackable (I only saw one in a price list). If you have a 3D printer another solution could be to make a clip-on hood with an extra overlap on the filter side to cover the edges.

I'm sure that would be a simple task for someone that understands 3D printing .
The top and bottom are unobstructed to enable the use of ND-Grads .

DREW WILEY · Apr 27, 2018

Of course, I've heard of a lot of people using TTL meters in both small film and digital cameras to allegedly determine large format shots. Some even use built-in
Smart(?)phone meters. I also know why these methods are less than ideal, especially if metering is done through a filter. I use Pentax spotmeters for all formats,
with appropriate filter factors. I once had a Minolta spotmeter too, and the readings were identical to the Pentax ones. I just prefer the rotating manual dial on the Pentax to the buttons on the Minolta.

neilt3 · May 13, 2018

Billy Axeman said:
Thanks neilt3, I didn't know they they were stackable (I only saw one in a price list). If you have a 3D printer another solution could be to make a clip-on hood with an extra overlap on the filter side to cover the edges.

Happened to be looking on SRB Photographics website ( formally SRB Gritturn) and spotted that they now offer a Cokin P size bellows type lens shade .
https://www.srb-photographic.co.uk/bellows-lens-hoods-1600-c.asp

Well worth using with the slot in filters to keep the sun off them causing flaire .
Even if your not using a filter but have several sized lenses needing different lens shades , this is a universal fit . Wide angle to telephoto , just pull to the disered legnth .
And folds flat for storage in your bag .

Billy Axeman · May 13, 2018

neilt3 said:
Happened to be looking on SRB Photographics website ( formally SRB Gritturn) and spotted that they now offer a Cokin P size bellows type lens shade .
.....

Thanks!

Vaughn · May 13, 2018

Doremus Scudder said:
Also a good possibility! Keep in mind that when using filters behind the lens, you'll need to focus with the filter in place to avoid a focus shift....

FWIW...I remember hearing that gels do not affect focus when used behind the lens, but glass ones do.

"Filters increase contrast" -- seems like students hear this and then expect the filters to be a magic bullet. They would slap on a red filter and wonder why the gray skies of coastal Humboldt County remain gray!

I have always liked how a yellow filter pops the yellow leaves of Fall under the redwoods (where and when I use one the most) -- and the yellow lines on the roads!

DREW WILEY · May 14, 2018

Fog? That's what auto-focus is for. Adjustable headlights.

My filters consistently decrease my negative contrast - what am I doing wrong?

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