Rokinon 135mm with aperture mask and normal speed filters - Forums

Topic starter

Dec 12, 2023

Ok… Rokinon 135mm f/2 lens. I have a step down ring of 58mm on the front as an aperture mask. No clue what that brings my lens down to aperture wise. If I use a normal L-eXtreme filter will it work? Camera is a 294mc if that matters and the actual aperture ring on the lens well be set wide open at f2. Trying to get rid of those starbursts I got when stopping the lens down with the aperture ring to f4… Thanks!

Benjamin

Benjamin DeHaven

Topic starter

Dec 12, 2023

Ok, I just went ahead and tried it. On the flame and horsehead I got signal, heart and soul I got signal, spaghetti nebula I got nothing in a test shot at 2 minutes and gain 400. So I think it works, not sure how much signal loss there might be but I'm not getting nothing…

David

Dec 12, 2023

Hi,
With a 58mm step down ring you will basically get an aperture of 2.3. It won't much improve your results.
Reducing the aperture in front of the lens will improve your stars shape (less diffractions), reduce achromatic aberrations, but won't improve the sharpness.
From my experience, best results can be achieved by closing the front aperture with 49mm stepdown ring, resulting in a f2.7 aperture.
You can also try by closing the diaphragm at f2.8 and compare the results.

David

Helpful Concise

Brandon Tackett

IOTD Staff

Dec 12, 2023 · Edited: Dec 12, 2023

@Benjamin DeHaven

I have been shooting with Rokinon for the past 3 years with good success. I stop my aperture down to f2.8 for star qaulity and still get great signal. I normal shoot with a efw with LRGB and SHO narrow astronomik 6nm filters. As long as your band pass is greater than 5 nm with single or multiple pass , it should allow for band pass shift at this focal ratio. My narrow band subs using a 294mm are usually 3 to 5 min. Hope that helps
-Brandon

Below are examples with the 135 and 294 mc osc