The Elements of Spacing

[John Austin]

I was about to sell a Shanel 5a shutter for cost of postage - So I Measured the Shanel shutter threads and depths for the almost lucky recipient and had a nagging sensation that the numbers were familiar

A quick look at my RD Artar showed my why - The RD Artar flange mount screws straight into the shutter, but with the rear component obviously removed - It will need a flange extension to work properly - Off to SKG for that one - After fitting the bits I removed them and checked them with a Vernier calipers, yes they did fit - (Is that the wrong way 'round)

Then I became silly, I screwed the aperture barrel with front lens component into the front of the shutter and the rear component of the 19" RD Artar into the rear of the shutter, adding 33mm to the separation and moving the aperture away from the centre of the components and had a look through a camera - To my amazement an almost useable image was formed at FA, which improved on stopping down - I was expecting the extra separation to give unusable results, but it will work

However, I won't try this set up with film in case I like the effect and start on the slippery slope of Galliography (Sorry Jim, I couldn't resist that one)

(Pix later as Rae has gone off with her digicamera)

The shutter sale is now off, to not do the sensible thing and put the lens and shutter together would be foolish of me, even with my beloved Sinar Shutter in daily use

The question is just how critical is lens mounting, spacing and centring? - For the last 45 years I have believed only the ordained high priesthood of repair men may open a lens, that is what some have told me over my open cheque book - Am I now guilty of heresy by thought and deed?

 

[John Austin]

Pic

View attachment 47638

 

[Ian Grant]

Some longer process type lenses from Zeiss used quite a thick a spacer which was used in place for normal copy work but could be removed for more distant focus through to Infinity. (It wasn't a spacing washer rather a small bit of tube that lengthened the barrel))

Ian

 

[ic-racer]

It looked like the shutter was buggered in that picture of the Schanel from the other thread, does the shutter fire ok? If you do decide again to sell it, I was wondering if it would mount my Fujinar 250. In this thread, Ben Syverson had a Fujinar 250 on a Schanel, but it looks like a different model than the shutter you have. I was also curious if you Shanel has an aperture scale.
http://www.largeformatphotography.i...m-f-4-5-what-should-I-expect&highlight=shanel

 

[Maris]

The question is just how critical is lens mounting, spacing and centring? - For the last 45 years I have believed only the ordained high priesthood of repair men may open a lens, that is what some have told me over my open cheque book - Am I now guilty of heresy by thought and deed?

In broad terms centring is critical but spacing is a variable available to the optical engineer and lens maker. Generalisations follow:

Increasing the spacing shortens focal length. Front element focussing lenses do this.

Symmetrical designs are less sensitive to spacing. Asymmetric designs, retrofocus and telephoto, are more exacting

Long focus lenses are less sensitive to spacing than wideangles.

Slow lenses are more forgiving than fast lenses.

Changing the spacing can optimise a lens for different reproduction ratios.

The trade-offs between lens abberations can be adjusted by altering the spacing. In symmetrical lenses the balance between field curvature and astigmatism can be optimised by the spacing. Some lenses feature variable element spacing to increase spherical abberation = "variable soft focus".

Inter-element spacing is one of the "degrees of freedom" available in calculating a lens design. In principle the seven first order abberations require at least eight (more is better) independent variables (refractive index, curvature, thickness, spacing, etc) to be overcome.

 

[John Austin]

It looked like the shutter was buggered in that picture of the Schanel from the other thread, does the shutter fire ok? If you do decide again to sell it, I was wondering if it would mount my Fujinar 250. In this thread, Ben Syverson had a Fujinar 250 on a Schanel, but it looks like a different model than the shutter you have. I was also curious if you Shanel has an aperture scale.
http://www.largeformatphotography.i...m-f-4-5-what-should-I-expect&highlight=shanel

The shutter works perfectly, in the previous thread I was holding the shutter half open in the open-to-focus or B mode to show some wear of the paint in the blades

Given my surprise at a fitting that should have obvious I have decided to keep the shutter for field work after I have had threaded rings made to hold 420 R-Claron and 19" RD-Artar lenses ('though the Artar is less favoured as it is hard to change the aperture while looking at the screen unless I grow simian arms)

The Shanell I have is shutter only, without aperture, for use with barrel mounted lenses - I had a look on eBay to see how these shutters might be worth and saw one with an aperture, a much more useful design - The eBay one also had several mounting rings for various lenses

The one referred to on the LF Forum I have just had a look at was described as a 5-BS, mine is a basic 5-A

Thanks the comments on lens spacing, 'though I was aware of the sensitivity of wide aperture Leitz lenses to reassembly errors - I made the excusable assumption that all lenses were that sensitive

John

 

[David A. Goldfarb]

On my Busch Vademecum casket set there are spacers that can be used between the lens cells and the iris for better quality at the expense of coverage. Mounting the cells without the spacers is considered a wide angle configuration.

 

[Philippe Grunchec]

On my Busch Vademecum Satz 2, the spacers are missing: I guess they are difficult to find... Someone?