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ambroz
20-Apr-2009, 10:19
I intend to do 6x12 cm or 2x5 inch (4x5 inch half darkslide). As I hear, focusing short focal lenghts on a GG can be a problem. (I could use Horseman or Linhof panoramic camera with focusing mount, but that's expensive solution).

Does centerfilter helps?

What's easier: to focus 150 mm lens on a 4x10'' camera or 75 mm lens on 2x5''? At 2x5 there is less room for loupe at corners.

If it's easier to work with 4x10, then maybe I'll go that route.

What are your experiences?

Thanks.

Archphoto
20-Apr-2009, 10:26
For close-up's you will need a focussing back.

The distance between the lens and the object dertimens the magnification of your object, with the back you focus.

If you try to focus with your lens you will run into the situation that you never get your object focussed propperly.

Peter

GPS
20-Apr-2009, 10:36
I intend to do 6x12 cm or 2x5 inch (4x5 inch half darkslide). As I hear, focusing short focal lenghts on a GG can be a problem. (I could use Horseman or Linhof panoramic camera with focusing mount, but that's expensive solution).

Does centerfilter helps?

What's easier: to focus 150 mm lens on a 4x10'' camera or 75 mm lens on 2x5''? At 2x5 there is less room for loupe at corners.

If it's easier to work with 4x10, then maybe I'll go that route.

What are your experiences?

Thanks.

A center filter doesn't help in focusing as it darkens the lightest parts of the gg to make the illumination uniform.
Between the 2 lenses there won't be any difference to speak about (just 3 horizontally) in the angle of view.

GPS
20-Apr-2009, 10:42
And - hopefully you know that with the two different focal lengths the perspective changes a lot, even if the angle of view is similar. That too must come to your consideration about the use of these lenses...

ambroz
20-Apr-2009, 10:49
For close-up's you will need a focussing back.

No, I do landscapes.

ambroz
20-Apr-2009, 10:53
Between the 2 lenses there won't be any difference to speak about (just 3 horizontally) in the angle of view.

I mean: is it easier to deal with dim corners on bigger format?

GPS
20-Apr-2009, 10:58
I mean: is it easier to deal with dim corners on bigger format?

The difference in the fall off is the same as it is in the angle of view.

Bruce Watson
27-Apr-2009, 10:48
The reason it's more difficult to focus shorter focal lengths is because the image becomes very small and thus the detail you are trying to focus on becomes more difficult to see on the GG. What tends to help is more light which is one reason why people like f/4.5 vs f/8 lenses, and more magnification from the loupe. I found increasing magnification just a bit, from 5x to 6x was enough to help me nail the focus from my 80mm lens on 5x4.

I suspect that you'll find it easier to work with 10x4 simply because the image on the GG will be larger, so the details you are trying to focus on will be larger. OTOH, you'll have somewhat reduced DOF because you'll be using twice the focal length for the same angle of view. So it's a trade off.

ambroz
29-Apr-2009, 02:00
Thanks for all comments. Any other opinions about 2x5 vs 4x10 focusing?

Armin Seeholzer
29-Apr-2009, 02:31
In my opinion its a tiny bit easier on the larger one.
I use not always a loupe on my 8x10 but always on my 4x5.

Cheers Armin

jb7
29-Apr-2009, 02:52
And - hopefully you know that with the two different focal lengths the perspective changes a lot, even if the angle of view is similar. That too must come to your consideration about the use of these lenses...

You'll have to help me out here-
How will the perspective change a lot in the two examples mentioned?
That is, 150 on 4x10, and 75 on 2x5?

Sorry, just wondering if I'm missing something...

GPS
29-Apr-2009, 04:28
If you want the object to be the same size on the gg the different focal length causes differences in the perspective due to the different distance of the lens from the object. I think you know that...

jb7
29-Apr-2009, 05:10
Well I know that the only thing that determines perspective is the position of the lens pupil-
so if you require an object to image at the same size using two different focal lengths,
then you're choosing to move the camera,
which will obviously change the perspective-

I thought the question was about the choice between two different formats to capture the same view, though maybe I read it wrong...

rdenney
30-Apr-2009, 10:00
In addition to bringing a loupe (and I use a 10x loupe for critical focusing on 4x5), I also bring clip-on magnifiers for my eyeglasses. These are the same magnifiers used by jewelers and watch technicians, and usually include two lenses that together provide 7x magnification. The advantage to these in the corners of extreme wide-angle lenses is that you can incline your head into the direction of the light, which I find helps with brightness compared to a 10x loupe placed on the glass at right angles. I just adjust my head so that the fresnel (or grind) pattern is sharp to my eyes, and then evaluate the scene details.

The center filter won't affect focusing at the corners that much (where the filter provides little density). But it will make the central image darker and harder to focus.

Rick "the best focusing aid is a great focusing cloth" Denney