BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="Surveyor" data-source="post: 1348327" data-attributes="member: 50720">Hmmmm Ed; Regarding the questions above, from my limited experiance, I think the answer to both would be yes. In 1, when B was in front you would see a lot better test than the other way around. In 2, the one in front would account for (assume 8x with a 4x booster) 32x at the eyepiece of the booster while the booster aberrations would only account for 4x, and only then if the full aperture was used. If the 4x were in front the ratio would be 32x:8x but, again, the booster is stopped way down. I would think the max possible contribution of the booster in the first case would be 32:4 or 12.5% and 25% in the later case and since the booster is stopped down, the results should be considerably better since the front is at full aperture. This, of course, is my personal opinion with no evidence of fact and I would like to hear what the more experianced practitioners think about this. Some interesting points/questions you bring up. I will spend some time and go thru that section around page 52 again. I have read it before but did not think it applied at the time so I may need to look from a different perspective. Your last sentence did suggest some experiments though. I just took a camera and tried to take picture of the artificial star with the Promaster and a 10x40 Barska that I have used on occasion with low power optics as a booster. Unboosted they were fairly useless. Neither the camera nor the optics were good enough to blow pics up enough to see anything plus, not being used to that low of power, I overexposed somewhat, at 80x there is a whole lot less light. If I can get a good star test of the bare optics then the boosted test should compare. I do not know that I can do that though; I usually need about 80x to get a decent pattern. I do have some recent tests were I used the Barska as a booster. I have never tested it but from what I just did, it may be decent stopped down. I got good round image inside focus and could see what appeared to be the roof angle. I will try to test it soon and then put the Promaster behind it. I have a set of tests with the Barska behind the Promaster left tube. I have put some in front and back before in a round about manner. One in particular I can think of is the Ultravid 8x20. It star tested very well, so I have used it most of the time when I can use an 8x booster, but I do not remember if I ever reversed two common instruments but whatever was behind the Ultravid had to be worse than it was, I think I may have used a 8x20 Zeiss monocular. I have attached a Barska test unboosted but with the photo blown up a ridicules amount. As soon as I get a chance I am going to test it. I will just do quick checks if the results come out as I think they will. Just too much trouble to line up two optics and a camera, plus the camera usually does not see the same as the eye. It will be a little while before I get to this but I hope to do something by, or during, the weekend. A note of interest that I thought of. Resolution testing is not that much different since aberrations kill the resolution. I have an ISO paper on resolution testing that spells out the max. power in some conditions and conditions when a auxiliary scope should or should not to be used. This is the only “official” paper I have seen that describes the use of a booster. Have a good night.Ron</blockquote>

Verification