ST80 - insufficient focus travel

[Commanderfish]

Hi Dave, its not new from factory, it's used so after market mods could easily have been performed.  In fact I can see that the previous owner blackened the focuser edges and marked the straight through focal point with a marker! I can return it to the dealer but as above it looks like the previous owner flipped the objective.  Everything else is very sound on the scope.

By the way the GSO 2" focuser is really nice, I got mine used for £60, it is so smooth.  Interestingly, changing from the 1.25" focuser to the 2" GSO stopped vignetting that was occuring when my eye wasn't dead centre to the eyepiece.

[Dave In Vermont]

I love my 2" GSO Crayford dual 10:1 focuser and large fine-tuning wheel on mine.

I'd still suggest returning yours to Valahalla. You should be paid for undoing someone else's "modification" to make the scope work - not the other way-around.

Have fun,

Dave

Oops! Large-wheel in other photo.

 

[Commanderfish]

The lens cell was the right way round. Are we out of ideas?

[SkyBound]

Well I am, I really thought we had cracked it there...

[nightfisher]

5 hours ago, Commanderfish said:

The lens cell was the right way round. Are we out of ideas?

No not out of idea`s, its time to send it back

[alacant]

10 hours ago, Commanderfish said:

Are we out of ideas?

Almost. But in the SGL we never give up!  How about some measurements? Is it really a 400mm f5? Measure the distance from the lens to focus from a light source like we did in physics classes. Here's mine minus the dew shield, in focus with the guide camera. The rule is just forward of the st4 female where the sensor is located. The clear aperture is 76mm and the outer lens element is embedded 12mm from the front rim. So on this example, an almost perfect 400mm. Sorry about the poor quality. HTH. 

 

[John]

I tend to agree with Jules / Nighfisher, whatever is the reason, the scope won't come to focus when used in a normal fashion for visual observing so the seller needs to be involved now.

 

[SkyBound]

Yes, I tend to agree now

if you mess about with it too much, and the supplier suspects that you have tampered with it too much, they could refuse to refund, just send it back.....  

[alacant]

On 20/9/2016 at 23:00, Commanderfish said:

I'm trying to use a second hand ST80 for visual.

Hi. I'm assuming it's secondhand... Dunno...

[Commanderfish]

Second hand.  Definitely tampered with BEFORE it got to me - permanent marker in draw tube, blackened edges etc.

[nightfisher]

Get it sent back, buy the TS 80 F7.5 version and have a really good scope, your new focuser will fit the TS

 

[Commanderfish]

The TS's Focal length would be way too long, I'm planning on using this as a finder on my dob, need wider field from a shorter FL and low weight.

 

[Stu]

Have you spoken to Steve yet?

[Commanderfish]

I've been calling Steve but no answer.  Website says he's shut til October 4th!  I'm going to email so he's got something on his system.

[Commanderfish]

Steve replied, sending it back to him. He reckons some of these ST80s (quite possibly the one he sent me) are 'set up for auto guiding' and is going to check the focuser position.   I'm sure he's right, but I can't for the life of me work out how they change the focal point.  Can't see anything on the tube or focuser that looks like it's been changed/is changeable.

[brantuk]

1 hour ago, Commanderfish said:

some of these ST80s (quite possibly the one he sent me) are 'set up for auto guiding'

That's very interesting - it would save having to add lengthy extension tubes to get a guide camera to focus and help reduce flexure - highly usable imho.

[Commanderfish]

If Steve sends me a different one for visual and keeps this one, I'll let you know so you can email him if you like

Good scope, even better if you get a GSO dual speed 2" focuser  

[SkyBound]

I am confused by this, my understanding is that a focal length is the distance from the front lens to the camera or eyepiece focus point, so in the case of the ST80 that has 400mm focal length approx, it doesn't matter what you do to the scope, shorten, lengthen the tube,  longer or shorter focuser, the focus point is still 400mm from lens to camera / eyepiece...!

so if you shortened the tube, you would then need more spacers to get straight through focus, and if you lengthened the tube you would need less spacers, and yes if you lengthened the tube too much then you would get your problem, but the tube would need to be about twice the length for this to happen....!! And yours is the origonal length hence my confusion

so without changing the front lens, how can this distance be altered....or are you saying that maybe the front lens has been changed....?? ?

Or have I got all this wrong...?

[Dave In Vermont]

20 hours ago, brantuk said:

That's very interesting - it would save having to add lengthy extension tubes to get a guide camera to focus and help reduce flexure - highly usable imho.

Yes it certainly could be useful,  if you knew what was going on with the scope prior to buying it for visual usage. Perhaps someone could write an article on 'how-to' do such?

Have fun,

Dave

[AndyH]

4 hours ago, SkyBound said:

I am confused by this, my understanding is that a focal length is the distance from the front lens to the camera or eyepiece focus point, so in the case of the ST80 that has 400mm focal length approx, it doesn't matter what you do to the scope, shorten, lengthen the tube,  longer or shorter focuser, the focus point is still 400mm from lens to camera / eyepiece...!

so if you shortened the tube, you would then need more spacers to get straight through focus, and if you lengthened the tube you would need less spacers, and yes if you lengthened the tube too much then you would get your problem, but the tube would need to be about twice the length for this to happen....!! And yours is the origonal length hence my confusion

so without changing the front lens, how can this distance be altered....or are you saying that maybe the front lens has been changed....?? ?

Or have I got all this wrong...?

 

On 22/09/2016 at 07:02, alacant said:

Almost. But in the SGL we never give up!  How about some measurements? Is it really a 400mm f5? Measure the distance from the lens to focus from a light source like we did in physics classes. Here's mine minus the dew shield, in focus with the guide camera. The rule is just forward of the st4 female where the sensor is located. The clear aperture is 76mm and the outer lens element is embedded 12mm from the front rim. So on this example, an almost perfect 400mm. Sorry about the poor quality. HTH. 

 

From memory, the majority of 80mm binoculars have objectives which are around F4(320mm focal length).

Could this troublesome scope have, at some point in it's life, had the original 80/400 lens switched for a bino 80/320 ?? That is, lenses removed from cell and bino lenses plopped in, in their place?

Just wondering.

Andy

ps: Orion's website states the length of an ST80 as 15" long.