Infinity Issues: Baldix and Ennagon f3.5

[Russell W. Barnes]

Hello all, and a Happy New Year. 🙂

I recently bought a Baldix 6x6 with an Ennagon f3.5mm lens, to see if it would better the Mess-Baldix I already use with its Baltar f4.5 lens.

So far, it doesn't, and I think there may be an infinity issue. I took a couple of shots about f11 with the lens set fully to Infinity, and whilst the subjects, typically 60' to 500' away are sharp, beyond that is blurred. This certainly isn't the case when using the Mess-Baldix with the Baltar lens.

I've placed a bit of diffuse material across the back as a focusing screen on each camera, and I can't see much difference. I've only done this hand-held under a coat, though, so may need a tripod and cable-release lock to assimilate properly. A bright day would help too. I've also focused a lamp through the back of each camera with lenses at infinity and apertures wide open, and the spot focuses at the same distance.

The lenses on their respective bellows appear to extend the same distance from the film-planes and are perpendicular to them.

Is there any other reason which may give rise to this 'selective infinity' thing? I'm not convinced that the Ennagon f3.5 is better than the Baltar f4.5 if kept tighter than f8. Both cameras seem to handle subjects between 5' and 20' well enough at f11 - the aperture I use with my Sunpak 33 flashgun with ISO400 film in the camera.

 

[Sarcophilus Harrisii]

I'm not familiar with the camera. What is the focal length of the lens? Because you mention 500 feet objects looking OK, beyond that not so good. 500 feet is a pretty good start on infinity for most lenses up to 100mm or so and perhaps a little more. If 500 feet looks OK I would have expected very distant subjects to be fairly sharp also but you're suggesting otherwise. I can only interpret on the information presented, but based on this I wonder if the lens is set to focus a little short of infinity. If the zones of focus are even across the whole film frame it's one of the only things that might induce subjects at infinity to actually look worse than those at 500 feet (but even then except for very long lenses I'd have thought the effect would be negligible if 500 feet is looking acceptable).

I strongly suggest conducting a more rigorous inspection of focus accuracy through the lens with a tripod and ground glass, and a loupe is absolutely essential to get a decent view of critical focus at distance.
Cheers
Brett

 

[Russell W. Barnes]

Brett,

Many thanks for that. Both Ennagon f3.5 and Baltar f4.5 are 75mm focal-length lenses. I shall try the tripod / ground glass / loupe method as I was a bit 'casual' with holding the shutter-button, focussing, and covering the camera with a coat!

The lens turns smoothly enough and there's no play on it. The 'infinity' mark aligns correctly with the diamond pointer.

Here are a couple of shots to illustrate. Yes, I know... Stand-developing HP5+ in Rodinal isn't the best thing to do (tank farm shot)! The night shot was also HP5+ but was developed in ID-11 1+3.

On the tank-farm shot, the ditant electricity pylon behind the wall should be in focus, no? On the night shot, the street (middle) is sharp, but the tall building in the distance with lights on isn't as sharp as I think it should be.

Test Shot Infinity by Russell W Barnes, on Flickr

Carlisle Civic Centre by Russell W Barnes, on Flickr

 

[VictorM.]

This method works best for me: http://rick_oleson.tripod.com/index-123.html

Then I fine tune it for closer distances-usually about 10 to 15 feet, depending on the distances marked on the lens.

 

[Sarcophilus Harrisii]

Yes, I see what you mean. I think the next step is to use a distant target that is well defined, whether it is a power pole, bare tree (these can actually be quite good if they're a decent size and have a variety of different sized branches) or other object with hard edges. Then, looking through the lens with a ground glass you can ensure the lens is set to infinity and observe the effects of pulling the focus in and back to the stop. If distant targets are not snapping into focus when the lens hits the infinity stop this may need to be adjusted. I also recommend observing the effect of focus sharpness at different parts of the film gate (lest the characteristics of the lens itself are compromising sharpness) and also repeating your tests with the lens closed down a stop, and two stops (which, if there is a noticeable improvement in sharpness, may also inform if focus issues are in part down to the behaviour of the lens design itself). You could close the lens down several stops, however the view might not be bright enough to observe anything useful...worth a try to find out, of course.

Let us know how you get on please. Oh and happy new year to you also.
Cheers,
Brett

 

[Russell W. Barnes]

Let us know how you get on please. Oh and happy new year to you also.

Brett - many thanks for the advice. I shall of course keep you posted but it may take a little time to get a decent diffuse plate together. If I can't get ground glass I'll use some of that diffuse tape stuck on a sheet of ordinary glass. I have everything else, including sight of a distant electricity pole and tree.

 

[johnf04]

I made a "ground glass" from a piece cut from a CD case, rubbed on one side with an abrasive cleaner.

 

[Russell W. Barnes]

I made a "ground glass" from a piece cut from a CD case, rubbed on one side with an abrasive cleaner.

Thanks for the tip, there. 🙂 I had the lenses out and cleaned them, cleaned the shutter out (not a complete strip-down but the low speeds are now accurate and the self timer works!).

Decided to collimate the lens with my Praktica MTL3 and Carl Zeiss Jena Tessar 50mm, checked with my Pentax MX and 135mm lenses. 'Infinity' is with the Baldix lens right in, so I've set it there. I used a strip of unmounted 35mm slide-film wound onto two 120 spools and drawn tight across the film gate, as I reckon that should be the correct thickness in the correct position.

I'll use the abraded CD case in the morning to check at 10' (as near as I can mark to 40 x 75mm - actually 9' 10"). Don't know what I'll do if it's out, mind! I suppose any sort of optimisation on a front-cell focus three element lens is a bit of a compromise.