ollypenrice

I had an RC here belonging to a guest. We read the manuals, we watched the videos, we understood the theory, we had the tools (Howie Glatter) and we could not get it right. Random effects prevented the process from behaving as anticipated. One adjustment interacted with another unpredictably. For me, life is too short and rafractors are too good. Olly

That's a great use of the material and I wouldn't hesitate to go for it as you've done. Mine's about 2.2 x 2.5 metres and has resisted everything including a flight and crash landing when two crappy anchor bolts turned out to be tat and sheered in a violent wind. Once picked up and put back on, the steel chassis was entirely undamaged. Regarding the roof material, I'm totally and unequivocvally wedded to corrugated galvanized steel and won't entertain anything else here, having tried the usual alternatives - all of which are flawed. Corrugated steel is totally waterproof, effectively everlasting and can be bolted down hard so it will neither tear through its anchors nor fly off. While it is noisy inside as the rain hammers down on it, the idea that it makes a noise audible outside is pure mythology. Next big job here will be to get rid of the useless rubbery-plasticky corrugated sheets on the big robot shed and replace them with steel. In less than five years the synthetic ones have started to tear off and distort while my oldest steel roof, which will be fifteen next birthday, is still absolutely perfect. I just have rigid insulation panels on the inside to counter the condensation. Our system here is to house our astronomers in the farmhouse: how many bedrooms will you install under that magnificent roof in the observatory??? Olly

I think that's lovely. There is no getting away from the subtlety of genuinely three channel colour images. Olly

No, you're correct but I believe that this EP is gives the widest FOV possible in 1.25 format. There's a discussion here. It seems to me that the conclusion (you'll never find a consensus on CN!) is that the 32 TV Plossl will go as wide as is possible at modest cost, especially second hand. https://www.cloudynights.com/topic/510769-which-eyepiece-is-best-for-the-widest-possible-view-in-125-inch-size/page-2 The best bet, though, apart from cost, is to go for a 2 inch back and a long FL ultra widefield EP. Olly Edit: keep exit pupil in mind. Divide the EP's focal length in mm by the telescope's F ratio.

Yes, 1.25 is cheaper. In our 14 inch SCT we use a 26mm Nagler which gives clean stars to the edge to my eye. Probably the widest format you could obtain would be with a 32mm TV Plossl though there will be comparable modern EPs these days. Olly

Unless the design of the scope has been altered I think you can acheive the same FOV without the reducer as with it if you have a 2 inch visual back. The field is limited by the baffle tube in both cases so it can be reached with a widefield 2 inch EP at F10. Olly

It's not a mistake, it's inevitable. What is out there is too gorgeous to ignore. Olly

Scroll down this thread to Sara's link (Swag72) for the 'too near/too close diagram: This should be helpful. Olly

Ah, SGL is real, being made of real people! It accounts for about 98% of my internet existence. It would, indeed, be good to meet up. I would love to attend the star parties but, obviously, they happen when I'm working. The moon has the unfortunate habit of scuppering everyone at the same time... Olly

I did check your website when looking for info on the image circle and didn't find this, but I'm not of the internet generation and am capable of missing a virtual bull in a virtual china shop. My apologies. I've also been guilty of giving too much credence to Tak's claim of 44mm as being able to cover a 35mm (long side) chip. I'm coming to the conclusion that Tak's 44mm claim for the Baby Q is erroneous - a generous term. It seems that Sky Watchers' 43.26mm are significantly bigger than Tak's 44mm so good for the Esprit. All this gives me yet another reason for saying that I'd certainly buy an Esprit 150. Olly

I'd like to clarify that my recent Astronomy Now article, in which I argue, in effect, that a six inch class refractor may be all you ever need, was not written as a eulogy of the TEC 140. It just happens that this is the refractor I have. I don't doubt for one moment that the Esprit 150 would have supported the same argument. Olly

Nobody at all would have accepted the elongated, curved stars which Yves and I found using two different Baby Qs and two different Kodak full frame cameras. Neither instrument got anywhere near to covering these chips and this was unconnected with flattener spacing since we were working at native FL. I agree that vignetting and field curvature are unconnected. Our pair of old Fluorite FSQ106s certainly have a considerable light fall-off into the corners, though the stars are good. Flats do handle the fall-off which is considerable, around 23,500 for the centre against 19000 for the corners. The filters may contribute a little to this. I think that there should indeed be an unequivocal industry-wide standard specifying field curvature and light fall-off. But this is an industry of cats, not dogs, and is resistant to herding... Olly

The trouble is that we don't know these things till we try them. Tak claim 44mm for the Baby Q which, you might think, would cover full frame for the reason you mention. However, it doesn't, so either 44mm isn't big enough or Tak are incorrect. I think the Kodak 11 meg is actually closer to 36mm but even this information isn't consistent 'out there.' This led me to think that 43.2 wouldn't be big enough but, it seems, it is. Anyway, the Esprit will cover a DSLR 35mm chip and that means the new CMOS cameras as well - so all is good to go! Olly

It would help if SW published the details of the corrected circle! They do now say it will cover full frame, which generally means 35mm, so that's great. The only 'real world' camera which might need more would be the one using the 36x36 mm Truesense chip. (From memory I think that this claim is a fairly recent addition to the SW literature but I might be wrong. I remember looking for this info some time ago and not finding it but I can't find my slippers or my mobile either...) I think the Esprit 150 is a great refractor and, as I said earlier, I'd certainly buy one. Olly Edit: Yes, you are absolutely right. Nik Szymanek, who can be trusted, tested the Esprit 150 with a full frame DSLR and found it covered the chip perfectly. My apologies for questioning this. http://www.opticalvision.co.uk/documents/107.pdf

I wasn't thinking of vignetting but of well illuminated and well corrected circle. That of the TEC, for instance, exceeds the size of any chip I'm ever likely to be able to afford. But, if you don't need it, you don't need it - and the Esprit would give you more aperture for less dosh. Olly

The Esprits are certainly exceptionally good at the price. Often it's the size of the corrected circle which distinguishes the alarmingly expensive from the merely costly! I use two cameras in my TEC140, a small format and a large. I'd be perfectly happy to accept that the small one would probably do even better in an Esprit 150. The full frame chip does, I think, need the TEC. Would I buy an Esprit 150? Is the Pope a Catholic? Olly

There's a Photoshop fix as well. Copy layer, set top layer to blend mode darken, go to Filter-Other-Offset and experiment with a horizontal pixel offset. I went for 4 pixels and then used Edit-Fade to apply only 90% of that. It's thuggery, of course! Olly

You're right that there is a slight R/L elongation but it really is very slight. I think it's fine to try to get to the bottom of it but it would be a shame to let it spoil the image for you. Olly Edit: While we're being pernickety, I'd be very careful where you place your background markers in DBE because I suspect they might have been a tad too close to the galaxy. There's the tiniest hint of a dark ring around it, maybe? Or am I inventing it? ABE tends to do this on galaxy images, I've noticed.

It's a good result. Greens look a bit high to me. Dead easy fix with SCNR green though. Olly

You might be surprised by how small a roll off observatory can be. The most compact design is usually called the 'sentry box' with the entire shed rolling off when observing. This way the shed can be a tight fit around the mount and scope since it doesn't need to house the observer as well. Also they can be made incredibly easily: you start with a small concrete base and pier. You buy the smallest, simplest shed that will fit over your setup. These can be wooden, plastic or metal. You make a plywood floor the size of the shed's footprint and fit it with little wheels running on rails. It needs a slot cutting into the plywood floor to let it run halfway round the pier and then you just build up the shed on the wooden rolling floor. I've made two sheds like this but the simple idea of using a rolling floor to carry a standard bought-in shed didn't occur to me so I spent ages welding up chassis and frames myself. Curses!! ?lly

I hadn't read John's report before but it's first class and answers the question, I'd say! Olly

I think it's the seeing. It's exactly the same for us even with pretty dark horizons. Olly

Vlaiv is perfectly correct that the round stars test is almost meaningless but at least with round stars you can produce an attractive image. When setting up the first Mesu we always had round stars but by tuning the guide parameters they got smaller and smaller! I don't think there's any reason to believe that the HEQ5 is less accurate than the 6 provided both are within payload. Any backlash adds to the guide error and the worse the seeing the more it does so. (When corrections are few there is a reduced tendency for the mount to be sent oscillating across the backlash.) So losing the backlash is a very good idea. The other ways to combat backlash are to run slightly east heavy and slightly polar misaligned. East heavy keeps the drive in 'push' mode and the misalignment means you can disable guiding on one direction in Dec, letting the other 'push in the direction of correction.' This does work and won't stop you from doing 15 minute subs. The duration of guide subs is also something to tune in the light of prevailing conditions. Our EQ sixes thrive on short guide subs if the seeing is good because they have pretty rapid PE. However, if the seeing is bad this has them chasing it, so we do better with longer subs which average out the position of the guide star's image. (It's worth remembering that the guide trace has no way of knowing where the real star is. It only knows where its image is. So very short subs do give a better trace but is that a trace of the real star or just its image? Curses!! ) The other variable within the guide trace is the position of the scope between corrections. Again we have no means of knowing, but Avalon claim that with their backlash-free belt drive the correction is fed in faster so that, between guide inputs, the true location of the scope is on target for more of the time. With any backlash oscillation in play it's a good bet the situation between inputs will be worse. Olly

I also use the AP adapter and it would astonish me if AP didn't do a good job of blackening. They're a pretty serious organization. If using paint, be aware that you shouldn't use anything made with dyes, which are reflective in other wavelengths. I forget which. You need to use a paint made with pigments, such as high temperature paints for barbecues and stoves. There's a paper about this somewhere on the net. Olly

The theory is perfectly sound, I agree, but does this actually ever happen in practice? I use pretty much the same setup as the OP - sometimes exactly the same depending on which camera he's using - and I've never seen such an effect. I've also hosted two robotic TEC140s and, again, never encountered any refocusing effects on flats. Olly