Cannot get Focus

[menacegtr]

Hi again all of you. It's been about 3 years now that i have owned my Startravel 120mm, i still love and use it. But, i am miffed as to why i cannot use something like an OVL 45° Erecting Prism 2" or anything like it. I don't have enough inward focus to find long range targets during daytime i just run out of focus. I am using a OVL Dual Speed 2" Crayford Focuser to replace the standard item. Why can i not get enough focus. i ordered an Ostara 2" 45 degree dielectric diagonal this week but again it does not work. I contacted the shop i purchased it from and he was very surprised and said he has never heard this problem, so i sent it back today. can anyone here please advise why i cannot use this type of 45 degree diagonal. Thanks for any advise, help

[Peter Drew]

The reason is, as you have found, there is not enough in focus travel. An erecting prism requires extra in focus travel compared to an ordinary diagonal. You would have a much better chance of reaching focus with a 1.25" size erecting prism as it has a shorter light path than the 2" version.   😀

Edited August 14, 2019 by Peter Drew
typo

[Ruud]

Or the new focuser is longer than the other. Did you attach the new focuser as far forward as it would go? 

[menacegtr]

Thanks, that makes perfect sense. Why the hell didn't the shop owner tell me that when i rang up about compatibility with my telescope. I told him i already tried a different 45 erecting prism. Again thanks

[menacegtr]

2 minutes ago, Ruud said:

Or the new focuser is longer than the other. Did you attach the new focuser as far forward as it would go? 

Yes it was a direct replacement so it fits as the standard one did.