New Off Axis Guider

[dmahon]

Ie Convert male T to male 48, so a female T to male 48 adapter (like you said, doh). It can be had at zero length though.

http://www.teleskop-...ro-profile.html

[steppenwolf]

a female T to male 48 adapter ...... can be had at zero length though .

Aha, thanks for the heads up on this one. Provided it is fitted to the FR first, this is a possible solution - my only worry being that without a 'shoulder', in some circumstances, it could screw far enough in to the OAG to touch and scratch the prism. Handled with care though, you've certainly found 3.5mm of inwards focus travel! Thanks ....

[Tim]

Aha, thanks for the heads up on this one. Provided it is fitted to the FR first, this is a possible solution - my only worry being that without a 'shoulder', in some circumstances, it could screw far enough in to the OAG to touch and scratch the prism. Handled with care though, you've certainly found 3.5mm of inwards focus travel! Thanks ....

You are right Steve, I have one of these, used it with my TS OAG, and the only way to get it tight is to clamp it right in against the turret. If the prism was in the wrong place at the time it could get damaged/tilted etc. If it isn't tight, then the camera has the possibility of rotating. I gave up on mine in the end.

[steppenwolf]

Tim, thanks for that additional information. In your estimation, would attaching this to the FR's male 'T' thread first resolve the issue? I note that the ring in question has two slots for tightening it (or more likely loosening it!!) up against, say, the FR mounting face. I certainly don't like the idea of it pressing against the turret to secure it either!

[Tim]

It would depend on the thread length on the FR Steve, as the adapter will go to the shoulder on it, and potentially stick out past it. You could use those Baader spacers to bring the adapter to the end of the thread.

[Gina]

It looks like it should work with my ED80 FR/FF and Atik EFW2 with 314L+ but I can't try it because another adapter has "cold welded" itself to the FR/FF and being only thin metal and very short, there isn't anything to grip or drill holes into

[steppenwolf]

It would depend on the thread length on the FR Steve, as the adapter will go to the shoulder on it, and potentially stick out past it. You could use those Baader spacers to bring the adapter to the end of the thread.

Thanks for that, Tim.

I finally had the opportunity to try a test focus on the new OAG I have here and have adjusted the table down the turret so that the turret now projects 10mm from the table top. The optical blank on the sensor of my SXV guide head is set at 11.0mm from the camera face so I have 1.0mm of safety! The optical blank on the sensor of my SXVF-M25C CCD camera is set at 17.5mm from the camera face. With the SXV guide head at focus and the M25C spaced at 23.0mm from the OAG and also in focus, I have a sensor-to-focal reducer spacing of 59.0mm. My goal is 55/56mm so I have to find approx 3.5mm from somewhere. That somewhere is going to have to be taken from the FR to OAG region and by coincidence, the 48mm to 'T' adapter that I have is 3.5mm deep!! If I could safely replace this adapter with the shoulder-less one that Tim and I have been discussing above then I would have my perfect spacing of 55.5mm.

Needless to say, a shoulder-less 48mm to 'T' adapter is heading my way right now so I will be able to report further when I have had a chance to try it, notwithstanding Tim's timely warning about not tightening up against the turret!

[dmahon]

I use the SXVR-H694 with SX filter wheel and OAG. This gives a backfocus distance of 25+17+17.5 which is 59.5mm. Less the 0.5mm because of the glass filter.

Fortunately the TRF-2008 allows for 56+/-4mm - though as no-one serious uses DSLRs for imaging anymore it is annoying that manufacturers still design around the 55mm specification especially when it would be easy for any remaining DSLR users to employ a spacer.

You could always replace air with glass to get more backfocus.

[ollypenrice]

Agh, testing telescopes for imaging. Sometimes I could screa....

Ahem, excuse me.

Olly

[steppenwolf]

though as no-one serious uses DSLRs for imaging anymore it is annoying that manufacturers still design around the 55mm specification especially when it would be easy for any remaining DSLR users to employ a spacer.

I'm not sure that the DSLR's days for astro-imaging are numbered just yet but I certainly agree that it is an awkwardly tight spacing when you factor in filter wheels and off axis guiders. The trouble is that basing the spacing on a DSLR camera does at least represent a recognisable 'standard' of some kind. Whilst it makes plenty of sense to have a new, more generous spacing standard, what would we base it on as CCD manufacturers seem to have a variable range of sensor to mounting face distances?

[steppenwolf]

Yippee, I've cracked it!

With the shoulder-less M48 to 'T' adapter at the front (suitably tightened onto the focal reducer's thread as discussed above) and that final 3.0mm extension at the rear (making 23.0mm extension from the rear of the OAG to the face of my SXVF-M25C CCD camera), I have a sensor to FR spacing of 56.5mm (just within tolerance) and both the imaging CCD camera and the SXV guide head in focus! I knew it would be tight but it is doable.

[Tim]

I don't know what the spacing is on the SX cameras Steve, (why oh why isn't there an accepted standard!) but on the Atik cameras, at least the 400 series, the space is 13mm, might be easier to achieve the spacing?

Clear here and the OAG is performing very nicely in situ

[steppenwolf]

My initial thought was that CCDs like the Atik with their shorter sensor to face distance would have an advantage here but sadly that isn't the case - the governing dimension here is that long turret length. No matter what camera(s) you have, the light to the guide 'scope has to travel from the focal reducer face to the centre of the prism (minimum 8.5mm) then up the turret (45mm) and then to the sensor leaving a safety gap of, say, 1mm between the turret top and the sensor glass assuming that the turret will fit inside the guide camera's throat.

The Atik's shorter face to sensor distance does give it an advantage in that the table can be set higher up the turret allowing the prism to be set further into the light cone if the imaging camera will allow it.

The good news is that it can be done but boy is it tight! SW focal reducer owners will have a much easier time as the FR already has a 48mm male thread, I believe.

One thing is for sure, it is worth working on because the OAG itself is excellent!

Sent from my iPhone

Sent from my iPhone from somewhere dark .....

[Helen]

So can FLO feed back to the manufacturer that a shorter turret would make this a real winner :-)

Helen

[Freddie]

Got mine set up now.

The trick is getting the correct spacers everywhere. With the MN190 I have needed to get everything as short as possible between the OAG and Atik to ensure I had enough inward focus movement to get that in focus. With that set, then needed a super short connection between the Lodestar and OAG to get the prism close to the Atik chip and get the loadstar into focus. Nice bit of kit though and definately no flex issues. As Helen has said, a shorter turret would be good.

[Gina]

What do you need to attach the Lodestar to the T2 OAG guide camera mounting? The QHY5 just screws on directly but I gather the Lodestar is different.

[steppenwolf]

The Lodestar has a 'C' mount thread in its throat but it is also the same diameter as a 1.25" eyepiece so it can be mounted in two ways:-

1. with a female 'T' to male 'C' mount adapter (not recommended because of potential spacing issues)

2. with a female 'T' to EP holder like this or this.

[Gina]

Thank you Steve I like option 2a

[Freddie]

I found I needed this to get the best fit.

http://www.teleskop-express.de/shop/product_info.php/info/p2838_Adaptor-T2-female-on-C-Mount-male---only-4mm-length.html

[steppenwolf]

I've now had an opportunity to use the OAG during a real session and it certainly didn't disappoint! I'm keeping this one! Taken with my one shot colour camera under a really bright Moon with constant clouds flitting by, here's my first image captured with the OAG in use:-

[Gina]

Nice one Steve I'm very pleased with the OAG and have now ordered a Lodestar and Baader focussing adapter to go with it Now looking forward to some clear skies

[FLO]

Steve Richards Off Axis Guider review can now be found at our Blog

[Tim]

Have used mine several nights now, and haven't experienced any issues whatsoever, there's certainly no flexing anywhere in the OAG that I can see, and the 3600sec (1hr) subs I took the other night bear out that conclusion.

[steppenwolf]

1 hour subs sound good to me!

Sent from my iPhone from somewhere dark .....

[Gina]

Excellent review Steve (Richards) with which I entirely concur - superbly made OAG