Thalestris24

I got the 2" EPs with each of the SW 130-pds and 150-pds scopes I think I got 1 6x30 finder with the 130pds - can't remember where the second one came from. I'll have to get the dust off and try and resurrect the 130pds one day...

I've ordered some from them - were shipped on the 7th Nov. Departed uk 'carrier facility' yesterday - I think that's probably Royal Mail. Should arrive in the next day or two! However, it's worth bearing in mind that they will be second hand lenses so no guarantee of quality. Hopefully good enough to prototype with and can be swapped later, if need be. The finder and ep doublets mentioned above are very good but a bit large in terms of diameter for the Lowspec design - would really need to make the design a bit bigger to accommodate them. As it is, it's not certain I'll be able to fit them in the optical path. I should be able to put everything together very soon so I'll know better then. Louise Ed. the mail follows a tortuous path in the States!:

Hi Dave In case you still need one, I found that a 2" 28mm EP has a 32mm dia f= ~70mm, achromatic doublet. Also, the 6 x 35 finders have 31.2mm dia achromatic doublets f= ~120-125mm, as objectives Louise

Edmunds are an expensive supplier - more for professional users, I think. Their slits do look more rugged, though. The Jeulin/Ovio one needs careful handling - as do all the spectrometer optics, of course! Louise

https://en.jeulin.fr/simple-radial-slits-212076.html I've only purchased mirrors and a reflective grating (so far) from Thorlabs. They are very good. They also send a box of 'lab snacks' with every order! Louise NB Jeulin charge more + shipping to export my total cost was £59.10 for the radial slit

This might be useful: http://www.awrtech.co.uk/telerrr3.pdf

Do you normally use an eqmod pointing model? I think eqmod saves that,so should be accurate, and I don't think there would be any problem using the same model data across different computers. It also saves the current position if you select it rather than home. The thing is, if there's a pointing error, where is it coming from? I reckon that's the puzzle you need to solve. If from the home position, you slew to somewhere else and then slew back to the NCP, is that then still the home position as far as eqmod is concerned? I'm sure you can solve this! Louise

Hi James Why do you think you have the problem in the first place? PA error? Or star alignment / pointing error? Something else? You can obviously correct PA error by drift aligning. I'd have thought that once that is accurately set, it should remain accurate. I only redo my PA occasionally and/or if I change or move something. If it's pointing error, then either creating a more accurate pointing model in eqmod (never done it myself). Or using platesolving should sort it - but you then have to make sure you use 'park at current position' rather than going back to the saved 'home' as that will lose the platesolving position - if you get my drift! I suppose if there's a problem as a consequence of returning to 'home' then lat/long settings could be made more accurate? Louise

Hi James I don't have a pier (I wish!) but I have limitations when it comes to alignment. My kit is semi-permanently set up. What I do is platesolve and then at the end of a session, I slew to a convenient position which isn't far from 'home'. Then I use eqmod to 'park at current position'. I find that it's then quite close to any targets next time I do some imaging. Having said that, I'm surprised you're a degree out - there must be an error in your home position? If you can correct that then I'd expect you'd be pretty much spot on from the get-go. Louise

Hi Jim For very short exposures at short focal length you don't have to worry too much about PA (see, for example, the 'no eq challenge' thread and others about alt-az imaging). There is a calculator here should you feel the need . PA error will show up as field rotation over time. The calculator assumes you are guiding and field rotation relates to how far away a guide star is from the edge of your imaging fov. If you are not guiding, and just tracking on an eq mount, and taking 30s subs, then I don't think PA will be your limiting factor. Louise

I dunno... I was only wondering if it was implemented on the gpcam3 178, but it doesn't matter really. Louise

As I understand it, it's about being able to stop the current exposure and start a new one. I get the impression it's something the imx174 can do http://www.scorpionvision.co.uk/industrial-camera-optics-blog/sony-imx174-sensor and also the imx178 http://www.scorpionvision.co.uk/_literature_152801/DMK_33GX178 .It's maybe a combination of hardware and software but I don't know if it requires extra hardware or not. It's really only a 'nice to have' and if you are only doing short exposures you can live without it. Louise

Oh ok, no worries - it's probably not a big issue anyway. Thanks Louise

Oh dear, I'm confused! Isn't the front side the shiny side? I'll have to look closer with a magnifying glass... Thanks Louise

Hi Ok, thanks Oh, re trigger mode - it's the electronics which allows you to interrupt the current exposure. So, if you had started a 60s exposure you can stop it at 15s, say. Without trigger mode you'd have to wait until the 60s exposure had completed before starting a new/different one. You'd notice this in SharpCap in the way it behaves when you try and change the current exposure time (assuming SharpCap supports trigger mode - it doesn't seem to with my qhy183m using the qhy Ascom driver). Louise

Hi Ags How are you finding the 178? Have you tried it bin 2x2? I was thinking of getting the cheaper gpcam3 version - I started a thread earlier but no response (yet). Does the zwo version implement trigger mode? Louise

Hmm… maybe a subtle difference but it's hard to tell under room light (my eyesight is poor away from bright daylight ). Both sides still seem reflective to a degree. So the idea is to have the front side, with the numbers correct, pointing towards the grating? Louise

I don't get it - mine is like a mirror on both sides? Am I missing something? Louise

I was thinking of getting a gpcam3 178m - anyone have one? I was wondering if the trigger mode is actually implemented on this particular camera. AA mention that their Hypercam versions have bigger electronics boards to manage the trigger mode. That implies that the gpcam3 doesn't actually support it even though the advertising blurb says it does (but we all know to take advertising with a pinch of salt...). It's not a deal breaker but I was curious to know. In any case, the camera seems good value for money. Thanks Louise

I think it's the dark side of the dark side! Louise

In an earlier post I reckoned a simple adjustable led would do the job but Ken thought illumination unnecessary - I'll try both . Also, I'm wondering if Ovio may have recently changed the design of their circular slit to make both sides identical ie both shiny? Were previous ones only shiny on one side? (I noticed there was a mark on one side of mine which is a bit annoying though won't affect the slits.) Louise

I guess you switch it off once you've lined up? What do you use for the illumination? Does the white slit back illuminator piece line up ok? Thanks! Louise

Actually, I just took my slit out and unwrapped it. As far as I can tell both sides are identical, both equally shiny. So it doesn't look like it will make any difference anyway. Louise

I believe you ha ha. Here is what my slit holder looks like without the slit fitted. I am a bit suspect of the back illumination part as it has a slit-shaped hole but the position of it seems offset a bit (maybe it lines up - hard to tell without putting the slit in). Anyway, probably best to leave it out altogether if not using the illuminator option? Louise ps I was thinking of spraying the inside with matt black paint as there are some shiny reflective bits in the black plastic?

Hmm... Paul Gerlach's design and assembly has it with the shiny side facing the guide mirror - isn't having the reflective side being seen by the guide camera how the reflective slit principle works? Now there is after the slit an aperture in the plastic which contains the slit illumination part. I'm wondering whether that might interfere? Louise