Willam Optics Star 71 5 element Apo Astrograph

[gnomus]

Thanks Dave.

I am sure I read that some of the CCD guys were discussing back focus of 55mm? The camera comes with a 2" barrel adapter which I will have no way of attaching to my M48 male thread adapter so I will need something. There is a M48 0.75 thread short adapter so this would work I guess...

As you say I wont be purchasing anything until I have the camera but it will be good to get this information ready as I have found on numerous occasions that there is rarely a "standard" setup with any Astronomy gear.

I currently use the supplied Canon M48 adapter ring with my Canon 1100d when attaching it to the Star 71. I find I have to extend the tube out to around the 17th mark on the telescope.

This is in stark contrast to what the CCD may require where 5mm is mentioned?

As Davey says you only need to be concerned about spacing if you are using a focal reducer. The Star 71 does not require a focal reducer. The only issue therefore is will it focus. I have an Atik 383L and an Atik filter wheel. I get focus at around half the total travel of the focuser. I don't see there being a problem.

As to the correct adapter, you could do what I did - e-mail FLO and get them to send you the ring that you need. That seems to work every time.

[DanL]

Can't comment on the Star 71 but my G2-8300 came with the short thread M48 adapter which I requested at time of order. Not that I've actually been able to use it yet. I might have to emigrate to southern Spain...

[Droogie 2001]

Thanks guys. At least I have a number of options available. That's ticks off another part of the upgrade plan.

[zicklurky]

I just got a Lakeside motor focuser and after a bit of confusement I got the big focus knob off like so:

Remove the grub screw closest to the focus knob. This reveals a hole, with the focus knob shaft inside. This shaft has 2 grub screws, 90 degrees apart, which need to be loosened to remove the knob. Turn the focus knob until a grub screw appears in the hole, and loosen it slightly. Turn the focus knob again until the other grub screw is visible in the hole, and loosen. The focus knob will slide off.

Hope this helps someone.

[Droogie 2001]

If anyone is interested as I have just found out much to my frustration a Moravian G2-8300 Mono with internal filter and a WO Star 71 will not focus stars with a short thread M48 attached.

I have moved the focuser to the max 35 scale and the stars are still not focused. I have requested a M48 55mm BFD adapter from my supplier.

I just hope this is sufficient because I am at my limit with this purchase. Despite all of my preparations I have had nothing but frustration with setting the OTA, CCD and mount up together. I knew the CCD was going to weigh a lot more than my DSLR but with this and the back focus the balancing in DEC needed a lot of work.
I find that my Celestron AVX (yes, its next for upgrading...!) will not balance in DEC with the CCD attached. It does not matter how much you move the existing Star 71 dove tail up the vixen saddle it is way too short. The other issue is that the WO Star 71 has a very large and obtrusive focus locking screw which limits how far you can move it up the vixen saddle. So I have to buy an ADM vixen dovetail long plate (I have read some people have mounted their Star 71's upside down to overcome this?!)  Then I spent a week working out what size screws I needed attach it. Non standard sized ones were of course the answer.

This thread gives you more of an idea of what to expect though this is with a different model of WO.

https://stargazerslounge.com/topic/256306-williams-optics-gt81-balance-probs/#comment-2799731

I am sure the fact I am using an AVX does not help but in standard spec the mount can handle the weight for imaging.
That said with all of guidescope, CCD, OTA, guide camera, original dove tail and ADM vixen plate (this weigh over a kilo!) it weighs in at 5.6Kg. This is still under the recommended imaging amount for the AVX but anyone considering buying a CCD for their Star 71 should definitely give all of these other factors serious consideration before purchasing. In my case I couldn't find anyone who had the exact same setup so I have had to learn the hard and frustrating way. Just hope I can sort this or else I don't know where to go next.

The 55mm BFD adapter is just going to add pressure /weight on the DEC again and once again I am beginning to reach the limits again on how far I can push the new ADM plate.

Anyway hope someone finds this useful.

[Droogie 2001]

Here is an image of the back focus short fall. Its getting close to focus but clearly still a way to go. Just hope 55mm is enough...

 

[gnomus]

With my WO Star 71 and Atik combo I have to attach about 1 kg in weight to the bit of the Losmandy plate I have sticking out in front of the saddle.  It is interesting that you cant get back far enough.  Mine is so far forward that I could not get an OAG to fit in (you don't need an OAG with the Star 71 but I was trying to get my camera to be 'dual purpose' with my SCT - ah well, another plan bites the dust).

I have my telescope 'upside down' ... but then again ... what is the right way up?

[Droogie 2001]

Its just a frustrating experience. This scope is labelled as an Astrograph and yet there seems to be an endless battle with trying to get it setup correctly for AP.

The focus locking screw gets in the way, the stock dovetail is too short with no ability for mounting it differently on the stock dovetail. The focuser dial gets in the way for mounting it further up the mount. Other people have struggled to mount auto focusers, the dew shield is too short and finally there is still no manual after 2 years! The fact some people have had to mount the scope upside down seems to confirm this.

I appreciate that WO cannot possible account for the hundreds / thousands of potential configurations but perhaps a redesign would help. I had heard that the Star 71 is not being made anymore so maybe its replacement will address these issues.

That all said the scope is regarded as a very capable OTA for the price.
I am sure I will get the issues sorted but it has been far from an enjoyable experience...

[Droogie 2001]

9 hours ago, gnomus said:

With my WO Star 71 and Atik combo I have to attach about 1 kg in weight to the bit of the Losmandy plate I have sticking out in front of the saddle.  It is interesting that you cant get back far enough.  Mine is so far forward that I could not get an OAG to fit in (you don't need an OAG with the Star 71 but I was trying to get my camera to be 'dual purpose' with my SCT - ah well, another plan bites the dust).

I have my telescope 'upside down' ... but then again ... what is the right way up?

Hi Gnomus

Would you mind posting a picture of the setup in particular the weight?

I know FLO do a bar levelling counter weight but I really don't want to add another 1Kg to my setup as I am approaching the maximum recommended imaging weight for my mount.

http://www.firstlightoptics.com/counterweights/baader-dovetail-bar-levelling-counterweight.html

Thanks

[AndyUK]

Hi Droogie - I don't have a Star 71, but I did have a similar issue with front weight balancing - I bought one of these

 

 

[Droogie 2001]

1 minute ago, AndyUK said:

Hi Droogie - I don't have a Star 71, but I did have a similar issue with front weight balancing - I bought one of these

 

 

Thanks Andy. How much does it weigh, 1Kg?

I cannot find the Baader levelling bar weights under this weight.

[AndyUK]

I just weighed it - On the scales the whole unit came out as 1.290 Kg...

EDIT - Ah, that may be too much for your mount .  But you could fit smaller weights to it(?)

[Droogie 2001]

Thanks Andy appreciate you weighing them for me.

Yes I probably only need a 0.5Kg weight the clamp of course weighs something, in your case 0.3Kg I guess? So maybe I go get away with an empty clamp!

I guess I will have to wait and see how much imbalance the M48 55mm adapter introduces, though I know it will be sufficient enough to bring it back out of balance.

[Robp]

I haven't experienced troubles such as you all have with my Star 71 and I am very happy with it.

I do hope you persevere and manage to get it sorted because it is a cracking scope once you get it going.

[AndyUK]

Hi Droogie - The clamp alone is 250g...

[Droogie 2001]

Okay so its an option albeit a gamble...

[Droogie 2001]

4 minutes ago, Robp said:

I haven't experienced troubles such as you all have with my Star 71 and I am very happy with it.

I do hope you persevere and manage to get it sorted because it is a cracking scope once you get it going.

Thanks. I realise some people will think that its my fault for mounting it on a low end mount (the AVX) but I know people with similar cost mount i.e. HEQ5 do seem to have had less issues in balancing...

[AndyUK]

I'm not familiar with the VX mount, but I see it's absolute capacity is stated as 14Kg... say 8-9Kg for imaging, or even 7Kg to be ultra-safe(?). 

I have a G2-8300 myself, and I know they're not light, but the spec for the Star 71 is pretty light (2Kg + rings/plate).   Can I ask what your current total payload is...?

[Droogie 2001]

Thanks again Andy.

I weighed all of the attached kit and it comes out at 5.6Kg. I think the recommend max imaging weight is half the absolute capacity so say 7Kg. So I guess adding a 1.2 kg counter weight as you suggested still brings it under.

 

[Droogie 2001]

Forgot to ask Andy but do you use an M48 55mm BFD adapter with your G2-8300 (internal FW?) and Star 71? How far do you have to extend the draw tube out on the Star 71?

[AndyUK]

Well, I do have a G2-8300 with internal filterwheel and I also have the Moravian OAG (which includes a 4.5mm spacer) and that gives me a total of 55mm...  but unfortunately I don't have a Star 71, so with regards to spacing I can't speak from experience (ie take this with a pinch of salt!), but I've had a look at the specs and these are my thoughts:

Looking at the Star 71 schematic on FLO, the backfocus from focuser to CCD chip would appear to be 66.4mm(?).  The Moravian/internal FW backfocus is stated as being 29mm, so, in theory, I'd say you should need another 37.4mm...

However, even with the focuser draw tube fully extended at 35mm, you're still obviously too short. 

If you added a fixed 55mm M48 though, and had the draw tube fully retracted, that would take you to 84mm, which, according to the specs would seem to be way too much...? 

My Moravian came with a nosepiece which is M48 threaded both sides and is 35mm long - Do you have one of those as well?  That would take your set up to 64mm which, theoretically, would be almost perfect as there's enough room for focus adjustment (2.4mm) but, being so small, that would then minimise the risk of any focuser slop (if there is any).

(Again, this isn't from any experience with the Star 71, only from the specs, so I'm a bit nervous about giving any advice here!)

[Droogie 2001]

Hi Andy,

I only have the M48 short thread adapter, nothing else. Do you have a picture? The G2-8300 cameras come with 2" barrel adapters is this piece you mean, it does not appear to have any threads on it though? I would have no way of using this 2" barrel adapter so the only option for me is the M48 55mm adapter.

The schematic you mention shows 66.4 as the distance so in theory I add the 55mm adapter and I should only have to draw the tube out to around 11.4mm? (Total= 66.4mm)

I need to measure the extent of the drawer tube as from looking at 33mm on a ruler I am sure mine is extending out further than that...?

Maybe I have completely the wrong end of the stick here?..

 

[PhotoGav]

I'm very sorry to hear that you are having such issues getting your Star 71 up and running. All I can say is that you really should persevere as the scope is a corker! I am getting to grips with mine and use a pretty heavy QSI 683-WSG with it. I did have to swivel the OTA so that the focus knobs are on the top and I put it on a long dovetail plate. It balances really well and easily like that. It's also very useful to have the focus on top as it is easy to get at both the stop screw and the knobs! Good luck and can you post a pic of your unbalanced set up? Here's a pic of my setup:

 

 

[Droogie 2001]

Thanks Gav.

Your tube seems to be only extending a short way out with no obvious additional adapters? I appreciate the picture is taken in day light so it may not account for accurate focusing. Do you attached the CCD via the M48 adapter?

I have attached a crude image with it loaded up. This was taken before I realised I had back focus issues.

 

 

 

 

 

[AndyUK]

Quote

The G2-8300 cameras come with 2" barrel adapters is this piece you mean, it does not appear to have any threads on it though?

Hmmm - Odd - Mine does - M48 male camera side and although the scope side is made to fit a 2" focuser, it has an M48 female... and it's length is 35mm, which would be perfect - It's a real shame yours isn't threaded . Mine looks exactly like this, but you might want to check the depth - 35mm max!

Quote

The schematic you mention shows 66.4 as the distance so in theory I add the 55mm adapter and I should only have to draw the tube out to around 11.4mm? (Total= 66.4mm)

Oooh - Careful...  The schematic shows the distance from the back of the focuser to the CCD focus plane.  With the focuser fully retracted, you therefore need 66.4mm from the back of the focuser to the CCD focus plane... BUT, you also need to take into account the distance from the CCD chip to the outer case of the G2-8300, which is stated as 29mm - With no spacers and with the focuser fully extended to its full stated 35mm, that would give you a distance of 64mm, which is 2.4mm short. 

However, you really don't want to extend the focuser all that way as it's almost asking for trouble (in my experience!), so if it were me, and going by the schematics and stated distances, I'd either go for the threaded nosepiece (if 35mm) or try and lay my hands on a (say) 25-30mm M48 adapter (I know Altair Astro stock a variable 17-29mm M48 as that's the one I have )