markse68

Trouble is the features on Mars are pretty low contrast- needs time at the eyepiece to begin to differentiate them. And time to get periods of steady seeing. Any fogging will ruin what little contrast there is. As will poor seeing conditions. Have you tried filters to help with contrast Neil?

Mark

I caught Io moving onto the limb and GRS transit but like you say it was too low to catch the shadow unfortunately. Here the seeing was very crisp and Mars looked good- I imagined I might have been seeing hints of Olympus Mons at times but the contrast wasn't good enough to be certain- probably imagining it  By the end I could scrape a layer of ice off the telescope tube but luckily nothing fogged up too much. Very fresh out there!

Mark

That’s very interesting Magnus and I’ve seen it too- though with my 8” f8 fullerscope the quality of which was unknown. It always showed asymmetry about focus in a star test except one night when it appeared close to perfect and that was the night i first saw the pup! Maybe i should look for a zerodur mirror  

Mark

17 hours ago, davidc135 said:

The rings shown in the out of focus Polaris images are Fesnel rings rather than diffraction. I'm definitely not an expert on the subject but the extra focus shadow seems a little larger and appears sooner than the intra focal shadow so, going on that, it seems a touch over-corrected. But that doesn't explain the sharper rings inside focus.

David

Hi David, I think the Fresnel rings are caused by diffraction from the aperture? Anyway thanks for your input- I know that mirrors can suffer over/under correction quite easily and commonly due to thermal imbalance and it may just be that- it was a sub zero night and although the scope was out for a few hours it may not have reached equilibrium. But i’ve seen the same in other nights so maybe it is baked in. None of the references i’ve seen show the double thick outer ring that i’m seeing which is the most confusing thing for me. Having said that they do somewhat resemble the images in Suiters book for spherical aberration due to under correction with a 33% obstruction (not sure what mine is- will have to check) where the extra focus rings are more blurry than the intra focus. But what you say about the central secondary shadow breaking out earlier extra focus tallies with what Suiter says about over correction too. But he warns “Ironically, the star test for spherical aberration is almost too sensitive. It is so revealing that nearly any telescope fails casual inspection” 

Mark

58 minutes ago, Paz said:

It would be useful to have an image or failing that if you can find an image of a star test online that looks as close as possible to what you can see and refer to that. Descriptions in words are difficult to interpret without leaving quite a lot of scope for misinterpretation.

Hi Paz, I posted a video- can’t you see it? I’m sorry i seem to be having issues with videos from my iphone not showing but i can see it on my phone and my pc.

Mark

On 07/12/2022 at 23:03, Don Pensack said:

I would give serious thought to returning it.

Thanks Louis and Don, I have decided to return it- too much trouble to try and rectify the issues and if it did turn out to be bubbles in the lens cement then impossible really. Shame as I had been after one of these for a while too

Mark

Hi Vlaiv, wont the drive whatever that turns out to be hold the position?

BTW what video settings do you use to upload embedded video like this? I couldn't get it to work at all

Mark

2 hours ago, newbie alert said:

Only getting the audio Mark...  What you're describing sounds to me like airy disc, where you defocus slightly to get the concentric rings, is that what it's trying to achieve?

Hi Newbie, yes sorry about that- it was showing on my iphone but not on my pc 🤷‍♂️ Have uploaded it to Flickr and embedded link that hopefully will work now. Yes it’s the diffraction rings of slight out of focus Polaris at high power (214x). Theory states that perfect optics will produce a perfect identical pattern both sides of focus- clearly mine isn’t yet it seems to work pretty well so interested in interpreting what it can tell about my mirror. Thanks for your interest

Mark

Superb!

currently observing Mars and Jupiter. Nice Ganymede shadow transit and tail end of GRS transit right now . Seeing is weird- the edges of Jupiter are swimming yet the surface detail is crisp! Jupiter still pleasing despite being past its best

Mark 

Thanks Mandy! I did briefly consider adding slomos to it but went for keep it simple and it’s working well as a nudge mount  

Mark

I’m in bortle 8/9 Louis and can confirm it works very well. It wont be able to plate solve at the horizon but the imu takes over then and keeps the map moving until it can platesolve again. If tracking starts to drift in accuracy  then you just have to swing the scope closer to zenith, let it sync again and off you go. It uses fairly long exposures so can see a lot more than you can.

Mark

31 minutes ago, Sunshine said:

Love the image but I am puzzled by your mount/tripod, the tripod resembles trusses on a dob, and the type of mount I cannot say I have seen, before.

Thanks Sunshine, it's an old military fire control tripod I had for years and finally found a good use for, and I made the mount to use with my Cape Newise but that has a fatal flaw yet to be resolved so for now it's supporting my Tal 150p

Mark

First proper clear night in ages- not sure it’s going to be wise staying up for the occultation though- work tomorrow 

Mark

Don't know about you but I find star tests very difficult to interpret even referencing Suiter's highly regarded book "star testing telescopes". Of course it doesn't help that the images are pretty unstable due to seeing and tube currents! If they came out text book perfect then I guess it would be easy...

So I thought it might be worth having a thread where we could post our star tests and get opinions on what they might mean? and hopefully learn from it. Would be great to see some excellent examples as well as examples with issues.

I'll start it off with my Tal 150p- a 6" f5 newt. Phone video of Polaris at 214x. I tried to move the focuser an equal amount either side of focus but it was just done by hand. I like this scope and think it performs very well. I'm getting nice detail on the planets when seeing allows and can easily differentiate the 4 Jovian moons by name. I guess that's all that really matters but the star test seems far from symmetrical. Intra-focal there's a thick outer bright ring then a thick dark ring then another thick bright ring, but extra-focal the rings are thinner and it's all a bit mushy and less contrasty. I think it is showing a slight mis-collimation but seems symmetrical so no astigmatism or pinched optics. I've read that seeing can cause differences either side of focus so maybe it's that but it has always looked like this whenever I've done a star test.

Mark

It’s no longer made so a bit unfair but I recently bought this seemingly pristine HD-60 25mm and finally had a chance to try it out last night. Pretty shocked at the QC!

The field stop is hairy! Looking closer there seems to be myriad tiny bubbles- I guess in the cemented elements though i can’t figure out how to open it to check. They reflect the light into radial “hairs”  

Even worse though is the 1.25” barrel. The nose is undersized at 31.65mm but the upper collar is 32mm- it doesn’t fit in a focuser. So the ep can’t be clamped without it wiggling about in the undercut!  

Its a nice looking ep and I had read pretty good reports about this series but this one is pretty awful!

Mark

Agree with all the points made- chancing on things that you weren’t even looking for is great and educating and being able to swing the scope back and forth between eg Mars and Jupiter in an instant is worth the price of admission alone I reckon. It’s a marvellous luxury!

Mark

Thanks Lukasz! Slim chances of seeing it though apparently possible if you get the terminator just right- I'd like to try. BTW I just had a look at your webpage and it is wonderful! 

Mark

PS are you planning to make a version of your very nice moon map using your own images?

1 hour ago, astrolulu said:

Only INA - a mysterious area distinguished by a blue tint, because of which it is sometimes called "Blue Lake", does not want to be blue... As usual.

Hi Astrolulu, where would Ina be in your image? It's another very beautiful image!

Mark

I think most Crayford focusers use a 4mm shaft or there abouts so about 12mm per revolution. Then either 8 or 10:1 reduction for the fine focus knob. I guess rack and pinions would use a larger diameter pinion so a bit coarser?

Mark

Ebay or Amazon?

Mark

Baader contrast booster can help on Mars. Televue used to make special Mars filters but you’d only find them 2nd hand now I think. Baader Neodymium is meant to help in general with contrast. I’ve been observing without filters so far this season but plan to give these filters a go again if the skies ever clear…

Mark

@Chriske has made loads of interesting 3d printed focusers- here’s a thread for inspiration if you missed it

Mark

Nice little scope Vlad. Your obsy looks awesome!- when are you going to finish it?

Mark

I agree with Peter- my skies would make star hopping with a Telrad impossible- some nights i struggle to see the main stars in Ursa Major. I use my red dot to quickly point at brighter objects then a raci for fine tuning, though usually the rdf is spot on. I occasionally use the optical finder for starhopping, though haven’t had a need to since i got a starsense. Actually, since i got the starsense i only really use the rdf when i haven’t bothered to set the starsense up as it’s even more convenient at quick pointing than the rdf. 

Mark