Help and comments regarding home made 4x5 enlarger

What is the reason, or what might cause, the projected image of a negative to be less sharp on a (hand-made) 4x5 diffusion enlarger than on a Gnome Universal Alpha II 6x9 condenser enlarger? The same enlarger lens was used in both cases.

The 4x5 projected image, though appearing bright and sharp seems to be very soft(???) compared with the sharp and hard image of a projected image from the 6x9 condenser enlarger.

The prototype diffusion 4x5 enlarger was made by cannibalizing an old 6x9 enlarger.
The 6x9 support for the [old] lamp assembly has been cut back to allow 4x5 projection. The lens holder fastened to the same 6x9 support remains, though the top section of the bellows disconnected.
The negative carrier is a piece of wood fastened on top of the modified 6x9 support [for the lamp assembly] using existing screws.
The existing bellows have been extended to cover 4x5.
The lamp housing is a substantial closed card box and the 60w incandescent bulb fitted at 90 degrees to the optical axis of the lens. A rectangular opening slightly bigger that 4x5 has been cut into the lamp housing and the interior of the lamp housing is covered with silver (cooking) foil.
The negative is held between a sheet of opal glass plate and a sheet of clear glass. This sandwich rests onto top of the wooden negative carrier; and the lamp housing fits on top.
By spirit level, the negative carrier is parallel to the enlarger’s base board; and is at right angles to the enlarger’s column.

Any and all comments welcome
Regards
Tony

If you've focused correctly, and everything is parallel as you say, then the image should not be less sharp. However, a condenser enlarger will project a contrastier image than a diffusion enlarger. Maybe you are just seeing the difference in contrast? Have you made prints and compared them? That will tell the tale.

Best,

Doremus

Quote:

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Originally Posted by Doremus Scudder

. Maybe you are just seeing the difference in contrast? Have you made prints and compared them? Doremus

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Hi Doremus
You could be correct, no I have not made a print.
The comparison was done using an image of a full sized pedal harp and looking at the strings on that harp.
It is more of an exercise to see what options I have - instead of buying a 4x5 enlarger [should I decide I want one].
The 4x5 enlargers I've seen are expensive, tend to be heavy, and some distance away.
I was offered a 10x8 De Vere (locally), but the practicalities of moving, installing and renovating were extreme.
Thank you for your response
regards
Tony
.

60W incandescent is likely a lot less light than the condenser enlarger - is that using the same bulb? - even without diffusion losses. Make sure you are comparing with equivalent baseboard illumination if you cannot make a test print. The difference could just be due to visual acuity at low light.

I agree with the suggestion to make prints, the appearance on the baseboard may be misleading, make a print using each enlarger so that they are matched for brightness.

Additionally, if the lens you are using was typical for 6x9cm then it would be around 100mm focal-length. Anything below 135mm is extremely unlikely to cover 4x5" so the lack of sharpness may be because you are not looking in the centre of the image, and hence are accidentally examining the image outside the effective object-circle of the lens.

For practical use, even with the right lens, there would be just about everything sub-optimal about your light system, but I understand this is just a proof-of-concept. There are some threads here, somewhere, about using Artograph(?) light-boxes succesfully as diffuse light sources for large-format and ULF negs. That might be worth a try.

I made a lightbox using an incandescent bulb for my graflarger when the original transformer died, and built a 5x7 enlarger on the same principle, and both worked as well as the graflarger. With your design you will have less light than you would on the 6x9, and I'm not sure what the impact of having opel glass in direct contact with the negative might be. On mine I used white acrylic, as I could not find opel glass in Thailand, and determined the correct distance from the sheet to the bulb by moving it up and down until not hot spot was visible. I also tried cfls, which are much cooler, but also more contrasty and less bright.

Somewhere on the forum is a thread about my 5x7 enlarger. Let me see if I can find it.

Here it is: http://www.largeformatphotography.in...e-5x7-enlarger

Hi,

http://www.largeformatphotography.in...arger-LED-head

:)