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Dallmeyer gauge projection lens
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PostPosted: Mon Mar 11, 2019 8:56 am    Post subject: Dallmeyer gauge projection lens Reply with quote

Hi, I am new here and new to manufocus lens. I have got few Dallmeyer gauge projection lens that I would like to make them work ( at least one of them). The only information that I have on this lens is 170mm and the measurement" target="_blank">Click here to see on Ebay.de of the outer ring is 59.3mm ( please see picture) , the body length of the lens 107.5mm. I have a fujifilm xt 20 and I do have m42 adapters. So, just wondering how can I make this lens work and what kind of helicoid do I need to get? Very appreciate with your help. Thank you in advance!

I am sorry, I put the pictures on, but seems not loaded up here.


Click here to see on Ebay


PostPosted: Mon Mar 11, 2019 11:20 am    Post subject: Re: Dallmeyer gauge projection lens Reply with quote

Flora wrote:
Hi, I am new here and new to manufocus lens. I have got few Dallmeyer gauge projection lens that I would like to make them work ( at least one of them). The only information that I have on this lens is 170mm and the measurement" target="_blank">Click here to see on Ebay.de of the outer ring is 59.3mm ( please see picture) , the body length of the lens 107.5mm. I have a fujifilm xt 20 and I do have m42 adapters. So, just wondering how can I make this lens work and what kind of helicoid do I need to get? Very appreciate with your help. Thank you in advance!

I am sorry, I put the pictures on, but seems not loaded up here.


Click here to see on Ebay


anti-spam-thing


PostPosted: Mon Mar 11, 2019 3:00 pm    Post subject: Reply with quote

To mount the lens you really want to know how far behind the lens it forms an image of things at infinity. A simple test looking at the distance the sky focuses at when you hold a piece of paper behind the lens is sufficient. I'd imagine it will be fairly well back for a 170mm lens.

Given the width of the lens it should be easy enough to fit it into a 65mm diameter helicoid (new ones on e-bay) or one taken from a suitably big old lens (with all the elements removed) Unfortunately the wider helicoid options are generally much more expensive than smaller options. It won't fit in any of the more affordable new helicoids (M42, 52mm & 58mm are all fairly reasonable). Of course you may be able to simply mount it in front of the helicoid, if the image forms far enough behind the lens.

The projector lenses I use all fit in a 35-90mm length m42-52mm helicoid which wouldn't be quite wide enough for your lens. A simple stepping ring stuck on the outside of the lens means I can unscrew one lens & fit another simply.

With some of my lenses an extension tube is needed for a useful focusing range (it can go either between the camera & helicoid or between the lens & helicoid). My 40mm perspective control lens needs extension while the 50mm/1.2 & 85mm/2.8 don't despite the fact longer focal lengths usually focus further behind the lens. The rear of my 50/1.2 actually comes out the back of my helicoid (& it's short adapter) for infinity focus - even after I trimmed a bit of spare tube away.


PostPosted: Tue May 07, 2019 5:14 pm    Post subject: Reply with quote

[quote="DConvert"]To mount the lens you really want to know how far behind the lens it forms an image of things at infinity. A simple test looking at the distance the sky focuses at when you hold a piece of paper behind the lens is sufficient. I'd imagine it will be fairly well back for a 170mm lens.

Can you detail the way how to figure out the flange focal distance. That really help to determine what helicoid is needed. Thanks!


PostPosted: Tue May 07, 2019 8:37 pm    Post subject: Reply with quote

cellotone wrote:
DConvert wrote:
To mount the lens you really want to know how far behind the lens it forms an image of things at infinity. A simple test looking at the distance the sky focuses at when you hold a piece of paper behind the lens is sufficient. I'd imagine it will be fairly well back for a 170mm lens.


Can you detail the way how to figure out the flange focal distance. That really help to determine what helicoid is needed. Thanks!

As described: use a sheet of something as a plane and focus clouds on the sky by simply moving your lens back and forth while the focus ring points to infinity.
The distance from the mount to the plane is then your focal flange distance.
Next you need to substract flange distance of the system you plan to adapt to, and what's left is a space budget for squeezing in a helicoid.


PostPosted: Tue May 07, 2019 9:16 pm    Post subject: Reply with quote

Got it, thank you! I had been using an adjustable helicoid by making it longer or shorter to find out the FFD, sometimes even needed a bellows. That helps! Thank you!


PostPosted: Wed May 08, 2019 8:55 am    Post subject: Reply with quote

cellotone wrote:
Got it, thank you! I had been using an adjustable helicoid by making it longer or shorter to find out the FFD, sometimes even needed a bellows. That helps! Thank you!


That approach is probably a lot more accurate, but having a vague idea before connecting the lens up can save a bit of time Smile