I have an ongoing focussing issue with my Meade Series 5000 80mm APO & I am very confused.
Bought the Meade second hand a few months ago & then purchased a range of eyepieces. The Meade comes with a 2" Meade diagonal & adapter to take 1.25" Eps.
Originally, I purchased a GSO Superview 20mm 1.25" EP (among others) but, could not get it to come to focus; not enough inwards travel on the focus tube.
I then exchanged it for a GSO SV 15mm 1.25" EP, tested it & achieved focus in the 2" diagonal. Problem solved, or so I thought.
Tonight I had the scope out & for reasons completely lost on me, I cannot get the 15mm GSO SV to come to focus; not enough inwards travel.
How can this be??
I simply don't understand what is going on here & it is messing with my head big time!!
Interestingly, a cheap HM25mm EP I have from a department store refractor comes to focus fine however, it is considerably smaller in construction than the GSO. All my other EPs work just fine.
Out of interest, the 15mm EP comes to focus just fine when used without the diagonal.
Could there be an issue with the focusser?
Could there be an issue with the diagonal?
Is this just an issue with these particular EPs design?
Should I switch to a 1.25" diagonal to shorten the light path?
Has anyone else had these issues with a refractor?
There is a huge amount of focus travel but, with the diagonal attached, the majority of my EPs only use the first cm or so of travel. Is this normal?
Hi Carlton, This might be a silly question, but have you checked that your diagonal is seating all the way into the focuser drawtube?
Some diagonals have a recess cut into the barrel for the focuser's compression ring to sit in, and this can catch.
Could explain why your 15mm eyepiece focused one time and not the next
Cheers
Also how high is the 2 inch - 1 1/4 inch adaptor ? eg how much does it stick out from the 2 inch diagonal when its fitted in .
5mm ? 10mm? , can you measure how much and let me know .
If its in the 5-10mm range its probably the culprit .
Adaptors are available ( GSO) from Andrews with only about 1mm stick out and they are recessed about 4mm so the eyepiece is closer to the objective allowing the focuser to be racked out quite a bit , about 6mm minimum more , which is all you need by the sound of it .
A photo of the whole set up as it is now , a nice close up of the focuser with diagonal and adaptor fitted will help a lot , as all eyepieces should easily come to focus in your sweet scope.
Post a photo here . .
Brian.
I will check that the diagonal is properly seated & I will post some photos of the whole rig in the next couple of days showing how much focus tube is showing & the diagonal with each EP in focus.
It's the 2" diagonal causing you trouble I think. A 1.25" prism diagonal has the shortest light path, which gives 45mm extra in travel (back focus) in my scope. A 1.25" mirror diagonal is less in travel than that but more than a 2" diagonal, which means you should be reach focus with your eyepieces. Try a cheapie mirror diagonal if you can and see if it works.
Matt
Despite woeful viewing conditions tonight, I did some playing around with my scope to see if I could achieve focus with the 15mm EP. The following is a synopsis of what I did & results.
1. Ensured diagonal seated home properly in focus tube. Not able to achieve focus with 15mm GSO EP, really, really close but, not quite.
2. Carefully disassembled focuser, screwed everything down firmly to ensure all firmly seated to OTA, reinstalled focuser & ensured that it was firmly seated. Not able to achieve focus with 15mm GSO EP. Again, really, really close but, not quite.
**Using the moon & then checking against a fleeting star (between clouds) I established that the 15mm almost looks in focus until you double check it against a star. This might explain why I believed I had achieved focus previously.**
3. I removed the 1.25" adapter (which has a 10mm lip) & carefully lowered 15mm EP into 2" diagonal. Hey presto, not far in it achieves focus. I estimate needing to lower this EP by approx 1 - 2mm in the LP to achieve focus.
I don't believe there is a problem with the scope. Although having a somewhat rudimentary understanding of Light Path mathematics & how focus works I think that if there was a problem with the scope it would affect all EPs, not just a couple of FL. It could be that this particular FL GSO EP (along with the 20mm GSO SV) just don't suit this particular setup.
Is this possible?
Options:
I have a few that range in not so expensive to relatively expensive:
a. Find a 1.25" adapter that has less than 10mm lip
b. Try different brands of EPs through trial & error. Could get expensive.
c. Try 1.25" diagonal although this is mildly inconvenient as I have a 30mm 2" GSO SV which works just fine.
d. Try Baader Hyperion EPs which can be used as either 1.25" or 2" Eps. This is moderately expensive.
e. Give up?? Not really an option.
What do you think is the best option; personally I think option A would do it but, not entirely sure what is out there. Any advice would be good.
Some photo's of the rig attached as previously requested by Brian.
1. 15mm GSO SV 1.25" EP inserted, not quite at focus but, no inwards travel remaining.
2. 9mm TMB Planetary 1.25" EP inserted, at focus. Approx 7 - 8mm of focuser tube showing.
3. 30mm GSO SV 2"EP inserted, at focus. Approx 12 - 14mm of focuser tube showing.
I ground the lip of a GSO 2-1.25" adaptor off and used a grub screw in place of the old screw. That worked well for my binoviewer and gave 10mm more in focus. Can post a pic if you want.
Matt
I ground the lip of a GSO 2-1.25" adaptor off and used a grub screw in place of the old screw. That worked well for my binoviewer and gave 10mm more in focus. Can post a pic if you want.
Matt
Thanks Matt,
I don't have a grinder to undertake that work but, appreciate the offer. I'm looking at the Televue in-travel adapter from BINTEL at the moment. Since only one EP is affected I figure I'll just put it on that EP & leave it there.
Might post a wanted ad, see if there is a secondhand one floating around in IIS.
Also how high is the 2 inch - 1 1/4 inch adaptor ? eg how much does it stick out from the 2 inch diagonal when its fitted in .
.
