sounds like you are going slow and steady then?
sounds like you are going slow and steady then?
No I think I'll put it on a camera first...just have not had the time to work on it
Newly made large format dry plates available! Look:
https://www.pictoriographica.com
First light!
Acquired a Burke & James press camera which accommodates a lens board sufficiently large for the lens. This allowed me to capture an image on one of my homemade glass plates coated with a homemade emulsion. This particular exposure was 3 minutes (it was getting dark) wide open at f/8.
I'm pretty sure my focus is slightly off due to the difference in distance from lens to the emulsion plane for a glass plate (0.050" thick) and for sheet film (~0.0075"). I focused the words of the license plate while viewing ground glass with a loupe to be centered in the depth of focus, but the license plate appears to be at the outer edge of the depth of focus in the image. The can blocking the plate number is about 6" wide and is completely within the DOF. Still, it allows some fair judgement of image quality -- which is close to prediction -- and bokeh, which is difficult to analyze in Zemax.
Next test will be for object distance much further. Or a portrait. I think this would be a good portrait lens.
Great job!
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
There is an online machine shop emachineshop.com which provides a design tool to use in designing parts and generating quotes. Perhaps that would be an option.
Someone asked the question about replacing the center lens with a custom one:
If you can get a custom lens made, use Ohara S-FTL10 or Schott K10 for the negative lens with the following parameters:
R1 = -65.25
R2 = 90.80
Center Thickness is 2.0mm.
Diameter is 36mm.
Grind a flat onto R2 for mounting. The clear aperture should be 32mm diameter. Sag will be 1.4208mm.
It is a concave-concave lens, but not equi-concave. R1 faces towards the front of the assembly and the orientation is important.
Other changes to the prescription:
Set the airgap (on the optical axis, see previous posts) between L1 and this lens to 9.5mm
I moved the stop to between this lens (L2) and L3. Bokeh looks better off-axis. It's more swirly than starburst like above with the stop between Lens #2 and #3.
The airgap between L2 and the stop is 2.25mm
Airgap from stop to L3 is 3mm.
Tolerances on airgaps are +/- 0.1mm, but hit the prescription values as close as possible.
This allows you to make a 177 f/5.6 lens. It will be soft wide open but will sharpen up on-axis quite a bit at f/8 and will be sharp across the field at f/16 to f/22. Distortion is < 0.5%
Here is the new prescription with a custom center (negative) lens:
Surf...R (mm)......T(mm)...Glass....Diameter(mm)
1.......64.38.........8.22......N-BK7...50.8......(Thorlabs LA1384)
2.......Infinity.......9.50......air.........50.8
3......-65.25.........2.00......K10.......36.0
4.......90.80.........3.00......air.........32.0
5.......Infinity.......2.25......air.........(f/5.6, D = 28.621)
6.......Infinity.......9.69......N-BK7....50.8.....(Thorlabs LA1050)
7......-51.50........158.15...air
f/5.6: stop diameter = 28.621
f/8: stop diameter = 19.84
f/11: stop diameter = 14.3742
f/16: stop diameter = 9.8604
f/22: stop diameter = 7.1646
f/32: stop diameter = 4.923
f/45: stop diameter = 3.5
This will give you a fine moderate speed 4x5 Cooke triplet with nice bokeh and soft portraiture if you shoot wide open, or a pleasing old-style swirly effect on landscapes that becomes less pronounced as you stop it down.
You could also mount the lens on a medium format camera to achieve a portrait focal length. I wouldn't shoot it with 35mm... it will be quite soft until you stop down to f/16 or f/22.
-Jason
Newly made large format dry plates available! Look:
https://www.pictoriographica.com
PVC pipe works pretty well. You can cut C shapes that spring fit inside the main barrel to hold elements in place and act as spacers between them. It's also cheap.Originally Posted by Will Frostmill
-Chris
I've sourced the custom element in Schott K10. In small quantities it's $110 per but there is a minimum order. Send me a message if you're interested. I am not selling this for a profit, just want to get costs down so I can afford a minimum order and figured there might be others who want to build this lens.
It appears it is time for me to clean up my old Sears mini lathe. Thankfully, they are still made under another name so parts and accessories are available. I Think I'll order a screw cutter today.
Original thread mentions 4x5. I would guess due to the off the shelf nature of the lenses, larger sizes (like 5x7) might be difficult/impossible? Curious because J's sample photo is BEAUTIFUL and it seems like this lens would be a lovely coupling to his dry plates if I can get a working ambrotyping process for those but was planning to do those in 5x7. And/or just wondering if it were possible.
PVC was mentioned which seems cheap and sensible but I was also pondering if some of the necessary support pieces could be 3D printed to perhaps make the process easier. If I get that far, I'll certainly keep folks in the loop on that.
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