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So--I came across this formula for determining the needed filter diameter. Does it look right to those who know? FD = ((Distance from filter to sensor/F-ratio) + (Sensor diagonal/2)) x 2 As focal ratio goes down--the filter size needed goes up. The problem I am having is I do not know how far inside the filter wheel the filter sits. So with a camera that has 17.5 mm backfocus (ASI 2600), using the ZWO 7 position 36 mm filter wheel--how far from the sensor is the filter. It will be 17.5 plus some number. The total thickness of the filter wheel is 20 mm--but the filter is close to the camera side of the device. I am thinking 5 mm....but I do not know and I need an exact number as it will be very close at F3 and F5 for 36 mm filters |
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I found this. It looks like for the FSQ with a .5x reducer and the filter 20 mm from the sensor a 34mm filter will work. So with the .6x reducer it will work even better--and native it will work even better. I was told the sensor is 20 mm away from the filter (by this table)--that is the key number in this equation |
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| I’m using the 36mm EFW Version 1 with the asi2600mm. First light was last night. I only see vignetting with the LRGB and not the NB and only when stretched in the ASIAIR. I’ve been told it will be calibrated out with flats from other users here. The camera which has 17.5mm sensor distance is attached with a 2mm adapter to the EFW. Then it’s probably about 5mm to the filter surface. So that’s approximately 24.5mm total. I could measure it but I just took flats and don’t want to unscrew everything until the EFW version 2 arrives. On AstronomyTools website it says the 36mm filters are fine for sensor size of 28.5 diagonal which is what the asi2600 has. |
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Brian Meyerberg: YAYYYYY. Now I can dream |
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| The EFW version 2 will bring the filters 7mm or more closer to the sensor. Less vignetting. |
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Brian Meyerberg: That's great--but I have to use the filter wheel I have. Only one configuration i have (FSQ at F3) will have viginetting, and it flats out. so thats ok) |
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Rodd, I'd be careful using that calculator. While I don't know the calculations used, it is disturbing that the defaults for the filter spacing do not change regardless of what camera you choose! Not all camera/filter spacing is the same, so I would expect the number in the calculator to change when you make a change to the camera and it doesn't. This implies that it is a field you must enter. The same holds true for barlows or focal reducers. Changing them does not change the focal length. Ron |
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NoRon: No but changing the barlow/reducer DOES change the end result of the filter size--so I think it is just a link between the focal reducer entry and focal length that is not working. But the filter distance is, as I said, the key in this table--I put a calculation to start teh thread I got from CN. There might be an issue with it though as the second parentheses set has a division by 2 that seems to screw with everything. It works better if the whole formula is divided by 2 --but I don't know. Can uou even input a distance for the filter in teh table? |
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| I was curious as well and have been tracking the details from people using both 36mm efw v1 and v2 (including details from ZWO). I decided to avoid any issues, future proof, and went with the 2”efw on my 2600mm. It’s been cloudy ever since... |
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After my first 2 imaging sessions with the asi2600mm and 36mm filters in the old ZWO EFW for 36mm filters I can say there is no vignetting at all. I saw a little in the flats when they were stretched but nothing shows up at all when you’re done stacking and calibrating. I’m extremely happy! No need to buy 2” mounted filters and a new 2” filter wheel which can cost an additional $2-$5G depending on brand. Here’s my 2nd Light with hardly anything cropped. Jellyfish Nebula |
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Brian Meyerberg: *** Yipppy, Yippy, YaY!!!! You have made my day. Very good to know. |
