Rusted

I have often placed a compact digital camera to the eyepiece of my telescopes to capture a 'snap' of the moon or sun. Something which I have yet to discover is a way to accurately calculate the true magnification of the optical system. My compact camera has up to 4 x zoom. Max 20mm f/l. Let's assume the telescope has an eyepiece fitted which provides [say] 50x. How do I calculate the system magnification as I zoom the camera to be rid of vignetting? Is it really as simple as 4 x 50 = 200x? Is it related to chip size? The camera focal length? The zoom factor as a simple fraction of the camera's max f/l? Or something else entirely? Thanks.

I'd try one of those long, thin things on a Berry-style, offset, counterbalanced, Dobby bearing, fork mount for small change in plywood. It's surprising how the moment [mass x distance from the axis] soon catches up with "inadequatorial" mountings. The moment of the objective & cell is effectively doubled because it has to be balanced [somewhere in the middle] by the focuser and finder at the other end. I have 90/11, 150/8, 125/15, 150/10 & 180/12 achromats. The difference between mounting the first and last equatorially is mind blowing! On Berry style altazimuths? Eazy-peasy! Provided you still have the strength to lift the OTA into the forks. 👴🏻

Thanks Dave. Totally overcast here now and getting windier. Rain promised for later. I blame all these airliners. It was a drought while they weren't flying! 😎

Thanks Richard. The dominant [dark] filament in the northern boundary of the "AR" shrank to almost noting in under half an hour:

The seeing was steady at first but soon became agitated. Still concentrating on the disturbed area in the northern hemisphere while it lasts. Well. you have to encourage the sun to put on a bit of a show, don't you?

Thanks. It is a delicate task to avoid an overblown prom when trying to bring out the low brightness areas. I don't have any special tools for darkening the background in PhotoFiltre7 after a bout with ImPPG. A flat might have worked but I am trying not to rely on them until I find a better translucent film.

The seeing didn't support surface features so I captured the prom instead. Swapped over to the PST BF in place of the Lunt B1200S2 which needs too much gain.

Thanks Peter. I keep trying!

The better seeing was short lived again. Chalk smudges coming out of AS!3 Only ImPPG could tidy them up. Using the T-S 1.6x Bino GPC again. The more northerly disturbed region is now huge!

Excellent set of images. Well done!

Thanks. I have just discovered a blind spot in my thermal deliberations. My large, pitched, shed roof is right beside the observatory on the east side. I have measured the sunny side of the roof at 50C! Eek! It's no wonder my seeing goes off so quickly as the sun rises! I'm thinking of replacing the tired, old, dark red, corrugated, fibre/asphalt. [Onduline.] Probably choose white painted, corrugated steel for lightness Though I have no real idea how cool that remains in practice. I'm just guessing as to its reflectivity in the infra red. Update: White painted steel is very efficient compared with most other materials: Solar reflectance up 80% and emissivity about 0.9.

Thanks. No idea what was causing the noise. Probably thermal? I am experimenting with shading the telescope objective when not actively capturing video. The ASI174 is showing 39C after not capturing anything for half an hour. So I have also closed SharpCap. The cloudy conditions are giving me time to try stapling some white shade material on the open shutters. I was seeing 44C on the shutters. Now I just need some sun to capture a few comparison images. Though It doesn't look any better on the monitor!

Early efforts were rewarded more than I deserve. I was saved by ImPPG. Then the cloud arrived! It's going to be one of those days! I am trialing my T-S binoviewer GPCs on the ASI174 1.25" camera adapter. 1.6x and 2.6x. Quite pleased with the variation in scale compared with my usual 2x WO Barlow. They offer useful variations in power depending on the seeing conditions.

Well done Den! That is a real piece of Solar art!

Thanks Mark. I just wish they were better. The seeing soon went off once the sun escaped the overcast. Perhaps I need a fan to draw air through the tube? Worth a try given how little work is involved. A suitable hole saw and Bob's your uncle.

Thanks Dave. Well worth a go right now if you can avoid poor seeing, cloud and chores. Proms as well as blobs.

Overcast until after 11.00. Seeing soon went south after that! Still a bit of cloud about. I'll keep trying. As you do.

You can't be too critical to have such a superb image of a globular cluster. As in: Spikes? What spikes? EDIT: Any shiny bits in the focuser drawtube or camera adapter tube?

Sorry to hear about this. These barstewards are anything but dome-esticated! GRP repairs are easy. External cosmetics sometimes less so. Tons of advice available but let's see what damage has been done first. Then we can move on from there. What about insurance? Any hope there?

For nearly two decades I was limited to an average of 120x on my 150/8 Celestron refractor. I couldn't ever see any detail in Jupiter's belts though Saturn was much better and Mars less so. The scope lived in an unheated shed so cooling wasn't a factor. Saturn was "orbiting spaceship" razor sharp, when high on one particular, cold night with an inversion layer and snow on the ground. Though Jupiter remained frustratingly fuzzy and "boring" on the same night. Which of them proved the telescope could be razor sharp? Swapping to a 180/12 iStar and putting it in a second floor wooden observatory literally doubled my average viewing power overnight. Telescope or seeing? I think I just lifted myself off the ground where the awful seeing was concentrated around my pier. Even when I kept moving it to different bits of the garden to see between the trees and high hedges. Those who suffer consistently from awful seeing might do worse than building a simple, raised wooden platform or raised ROR. Domes have their own problems depending on materials and colour. My supposedly poor 150/8 performed very well on the sun in H-alpha at high magnifications. Yet I was never very aware of its f/8 chromatic handicap. The Fringe Killer was always optional. The iStar 6" f/10 H-a which finally replaced it can capture Plato craterlets and did very well on a crescent Venus at first try. My 10" f/8 premium mirror [even badly collimated] Newt trashed them all. Even down on the ground. I read somewhere, probably 50 years ago, that the average UK seeing is in 10" deep layers. Which is why it affects larger apertures because the seeing varies across the aperture. So the optical precision of the larger optic is lowered in comparison with a smaller one. There are no fixed rules. Only local conditions, instruments and observers. Being rural detached and surrounded in fields is no guarantee of good seeing. Ask me how I know?

I find myself in some agreement with your arguments but not all of them. I swap back and forth frequently between my original PST BF and a Lunt B1200S2 BF. There seems to be no obvious logic to the correct choice. I just use the one which suits the conditions and subject matter at any particular moment. It takes only a few seconds to swap between them as I have the PST BF in a home turned sleeve in a 2" fitting. The B1200 sometimes offers startlingly better contrast than the PST BF on surface detail. At other times it is completely fogged out by ZWO ASI174MM camera noise due to excess Gain. The PST BF passes far more light than the Lunt 12mm BF. So I [usually] use the PST BF for proms. The Lunt is simply far too greedy for Gain and noise intrudes. At other times I cannot reduce the light throughput enough using the PST BF. Because I am down to 0 Gain and less than 1ms exposure in SharpCap. Typically I use 800x600 frame size = 400fps regardless of the WO 2x Barlow/GPC nosepiece being on the camera. Peter, very sensibly, does not image. His visual rig is the envy of all who have tried it. His vast experience at optics and instrument building puts most other humans to shame.

At 8 o'clock and 10 o'clock there are disturbances near the eastern limb with pale patches.

Good write-up! The Head Gardener suggested you hang the "Vegiebogie" under the tripod to get it off the ground. It might help to damp [off] the vibrations.

$600? 😱

I have an old 90M f/11 OTA presently "resting." [On its nose.] I wondered about the container behind the telescope in the image: Doing an oil change?