Padraic M

1 hour ago, Len1257 said:

Well when you have saved enough loot to buy 2/3 of a Senso Sesta just buy an ASI EAF and save the rest for other gear. I have one each on WO GT81, 150PDS with Baader Steeltrack Focuser, RC8 also with Baader Steeltrack Focuser. All work flawlessly with NINA.

Incidentally the size of the scope and flattener has little to do with what the focuser has to cope with. It's the image train that counts i.e. camera, filerwheel, OAG etc. You haven't mentioned that at all?

Actually a commonly-held misconception.

The ZWO from FLO, when you add the extra temperature sensor, hand controller and mounting bracket is €302 (£259), whereas the Sesto Senso from PLL, which comes with all of the bits in the box, is €245 €265.

Obviously customs duty may change the situation, but the PLL is cheaper than the ZWO ex-works on a like-for-like basis.

Flip a coin to select one I suppose, but I like that the scope can still be focused manually with the PLL in place (by turning the coarse-focusing knob) and it doesn't need a hand controller. I also like not needing a mounting bracket. It makes mounting and removing it really easy. I'm sharing one between two scopes at the moment (while I save for a 2nd one) and it's very easy to swap.

Edit: slight correction - the Sesto Senso doesn't come with a temperature probe so +€20 for that.

The PrimaLuceLabs Sesto Senso 2 doesn't need a mounting bracket, and is rock-solid on my scopes. Works well with Nina but won't work with ASIAir as it's not ZWO.

I got an Esprit 80 towards the end of 2020 and it's superb. Surely if you get a 'checked and tuned' version from a 'reliable supplier' 🙂 you can't go wrong?

Looks great! A new one for my list.

On 29/04/2022 at 10:38, Dave Lloyd said:

I don't think they will. They haven't even sent me my HST yet. 

I think there's one coming up shortly in the For Sale section. Collection only I'm afraid!

Nice gift! I think you should sell it to me and save yourself the bother of astrophotography. 🙂

All the important points are given above. Whether you go with ASIAir, mini PC or haul your laptop outside, you will need a EQDIR cable to connect to the HEQ5. Lynx Astro ones are great. Just make sure you order the one for HEQ5 Pro as the mount models have different connectors.

https://www.firstlightoptics.com/astronomy-cables-leads-accessories/lynx-astro-ftdi-eqdir-usb-adapter-for-sky-watcher-eq5-pro-heq5-syntrek-pro-az-eq5-gt-az-eq6-gt-and-eq8-mounts.html

My objection to ASIAir is that it locks you into ZWO products. Now that they've launched their own mount I wonder will they even lock out the Skywatcher mounts in a future version??? I use a Windows mini PC running NINA for capture control, but as mentioned above APT is great for DSLRs. I've used APT with a DSLR, but I believe NINA also supports them but it may depend on make/model.

You can polar align with your imaging PC. It's easy if it's a dedicated astro camera, but as you have a DSLR you need to jump through a few hoops to get SharpCap to work with it. There's some discussion elsewhere on the web on how to do that.

I'd suggest that you start with what you have and use your laptop until you know your way around; keep your subs short and stack them with DSS. Next priority would be to get yourself a guide cam and scope asap. They're not expensive and are a huge step up in performance. After that I'd look into an ASIAir or mini PC to avoid taking your laptop out into the cold and dew. The same EQDIR cable will work. In the meantime get a big plastic storage box to keep your laptop in while outside.

This is the results of OSC imaging from dark skies (B2) last night. The night started with really clear air and the darkest I've seen for some time. It did fog up a little in the early morning.

I also have a new processing workflow, using APP for stacking, Siril for background extraction, photometric colour calibration and stretching, and adding the final touches in Gimp.

I used the best 75% of subs to exclude the foggy shots. This is 39x300s subs for a total of 3hrs 15mins.

SW 150PDS, ASI533MC Pro @ -15c/gain 100/offset 21. Baader UV/IR Cut filter attached.

HEQ5 Pro mount, TS-Optics 50mm guide scope, ASI120MM Mini guide cam.

Captured with NINA and PHD2.

It sounds strange that you can't reach focus with that setup. Can you double check your measurements?

Let's take this as the distance from the prism centre line to the imaging sensor:
OVL OAG (13mm/2 = 6.5)---> 10mm T2 extension---> 10mm T2 extension---> ZWO 11mm Spacer ---> 294MC Pro sensor recessed at 6.5mm = 44mm.

The distance from the prism centre line to the guide cam must be the same to achieve focus. I don't have schematics for the OVL OAG, but the ZWO OAG has a 35mm stalk. I also can't find the size of the OVL prism so I'm assuming 10x10mm. So the equivalent measurement is:
OAG stalk length 35mm - half the prism depth 5mm + ASI290mm Mini sensor inset distance 8.5mm = 38.5mm.

This should give you 5.5mm to spare. One obvious question - you don't happen to have the ASI290mm 1.25" extension fitted? Worth asking! You could unscrew the protective window, that would save a few millimeters but would be a risk to the sensor. I wouldn't chop anything off the stalk!!!

Reference pictures here:

4 hours ago, newbie alert said:

You can't put the prism in that  yellow line position

I wasn't implying that you could... just showing the level to which you should insert the prism stalk.

.

What I understand tooth_dr to be saying, is that if you don't need the ability to rotate your sensor relative to the OAG, you can butt the prism right up to the long edge of the sensor like below. The usual advice is to push the prism in until you can see its shadow in a flat frame, then retract slightly so that it clears the light cone. The long edge can be the top or bottom edge of the sensor, it doesn't matter. This gives the best illumination of the prism, and lets it pick off guide stars closer to the optical centre line where they are most likely to be well-shaped and bright.

Putting the prism in the outer circle like you have above is only needed if you have a rotator between the OAG and camera, where you could potentially have the prism at one of the sensor corners.

2 hours ago, RobST said:

ZWO183MM

(I presume you meant MC rather than MM?) Agreed, but considered a little old-style at this stage because of the amp glow. The 533, apart from the square sensor which some don't like, beats it on all measures and has no amp glow. State of the art now though is the ASI2600 if you can afford it, or the RisingCam equivalent at half the price. People are getting some spectacular results with that sensor now.

You might need to question your opening assumptions. Andromeda is an unusual DSO given its large size. Most DSOs are much smaller, so going for a set-up that optimises for Andromeda will leave you too wide field for almost all other galaxies. Planetary nebulae will be tiny. Only the larger nebulae, supernova remnants and wide-field space shots will be suitable. For that, most people go with a shorter focal length scope or even the Samyang. No real need to go for an expensive full-frame sensor.

Take a look in the field of view calculator for other popular DSOs like M51, M27, M3, M57, Bode (M81&M82), Leo Triplet M65&M66, Bubble Nebula etc. They should all fit comfortably, if a little small, into your 90mm scope with the ASI533, whereas with a full-frame they will be lost. For larger DSOs like M31, M42, M45 etc., you can always do mosaics.

With a longer focal length scope you limit your targets, and the difficulty level goes up a couple of notches. Same for fast scopes - all margins become critical.

For a quality AP setup to get your teeth into, you'll find it hard to beat a EQ6R, Esprit 80 or 100 APO refractor, ASI2600MC Pro. Don't know what that adds up to but it would keep you happy for many's the year while you buy the add-ons, and you certainly won't be able to blame your kit for any poor quality images. Actually for this, the EQ6R would be a little overkill but it will stand to you when you get that EdgeHD or 10" imaging Newt.

Unfortunately the add-ons will be the other £5K 🙂. PSU or battery, Pocket Powerbox, Guide scope and cam, electronic focuser, mini-PC, LP filter(s), processing software, rotator, dew heaters, flat-panel, carry-bags, tube rings and Losmandy dovetail bars. All adds up. Some are optional but desirable. 

Then you'll want a mono camera (ASI533MM Pro just announced?), 7-slot electronic filter wheel and LRGBHaOiiiSii filter set.

Does that help at all??? 🙂 

Looks very similar alright but that's pricey! You'd almost be better getting it shipped.

Just consider it a feature that makes solar observation much more realistic 🥵🥵🥵😀

Yeah there have been lots of problems with that type of generic power brick.  I have one myself 10A 12V but it gives similar results. You will need an upgrade! If you have a second one you could try powering the mount directly with it. 

The Pocket Powerbox is a power controller but it can only control the power provided by the supply. if you're only getting 11.8V then your power supply isn't providing enough juice to the PPBA. You need to get a beefier supply - 5A or higher, and preferably 13.8V rather than 12V. The voltage will drop once you start to draw current, and the HEQ5 gets very edgy at around 11.5V.

You don't say what PSU you're using. Many of us use Nevada Radio supplies - either the 6-8A one or the 30A that I use. FLO supply both. The PPBA is perfectly capable if it's fed with enough power.

Stuart, maybe you need to try it out! I found it quite confusing the first time out and it took a lot of experimentation and mistakes to get it right (C8 XLT + FF/FR + TS-Optics OAG) but I think the guys above and James Lamb have covered it all.

If you're not using the 0.7x reducer (and I believe you're not) then it's more straightforward but still not simple. The James Lamb video is pretty good - I had to draw my own CAD diagrams (I did it on paper) to know exactly what distances were available, but the critical part is that the distance from prism to imaging sensor is the same as prism to guide sensor. Focuser goes ahead of the entire assembly, whether that's the EdgeHD primary mirror or the Diamond Steeltrack. The design of the OAG may constrain you somewhat - the closer the prism is to the imaging sensor, the further in to the OAG stalk the guidecam needs to be inserted. You may not be able to insert it far enough; if so you'll need an extra spacer between OAG and imaging cam to give some extra room.

If you're using a filter wheel or holder it goes between the OAG and the imaging camera so that you're getting full non-filtered illumination on the guidecam sensor (especially if using narrowband filters). James Lamb's proposed arrangement of imaging camera-filter wheel-OAG-spacers-telescope makes a lot of sense and that's what I've used.

I use the 290mm Mini guidecam and have never had to search/rotate for a suitable star. PHD2 is excellent in guiding on the oddest shaped stars, including bean-shaped and seagull-shaped. It also doesn't need focus to be spot on. If you use parfocal filters the small difference in optical path length through different filters shouldn't impact you.

Your focuser must go between OAG and telescope, because if it's between OAG and imaging camera it will change the critical distance between prism and imaging sensor, but the distance from prism to guide cam sensor will stay the same (the two cameras are no longer parfocal).

If you decide to add the reducer all of this will change and your distances will become more critical, as the back-focus distance from the back edge of the reducer to the sensors (both cameras) must be 146mm. You will not be able to put the Diamond Steeltrack, Crayford or R&P anywhere between the reducer and camera as it will change this back focus. I don't believe it can go ahead of the flattener (i.e. scope-side) either so you may be stuck with focusing by adjusting the primary mirror. (As I'm writing this I wonder does the EdgeHD have a built-in flattener with a fixed back-focus?)

Finally, when you have it set up correctly, try to keep the entire imaging assembly intact even if you take it off the scope. One advantage of the OAG setup is that once the two cameras are set correctly you never need to adjust them again. 

Pegasus Astro do an interesting OAG with a focus motor on the stalk. This gives more automation than most of us need, but sounds like a good idea for remote setups if the OAG could go out of alignment.

Best use for a pair of Marigold house gloves imo 🙂

Thanks for that. Also good to see where you're measuring from.

5 hours ago, Same old newbie alert said:

So after much too-ing and fro-ing, I decided to adjust it to work at the spec'd focal length, ie 1280... So I increased the spacing which reduced the focal length.. now I'm working at 1280mm and stars look much better..

Just to be clear with this - are you getting 1280mm focal length and good stars at 85mm back focus?

I spent some time trying to image with the C8 last year but didn't persevere. There's a lot of confusion around what the correct back focus is, as other sources contradict what TS says. Unfortunately the manufacturer is silent on the matter. Incidentally, the TS item is branded TSOptics, but it looks identical to the Celestron one so I assume it is actually the same reducer.

For instance, Agena Astro have information on back focus https://agenaastro.com/articles/a-primer-on-back-focus-in-astronomy#components. This says:

"When the f/6.3 reducer/corrector is used for imaging, we need to work with its back focus - or what’s really its specified working distance (see Section 3.2). This distance is 105mm for Celestron’s reducer, much longer than reducer/flatteners for refractors. To use a DSLR and T-ring (which have an optical length of 55mm), it’s necessary to add a T-adapter tube with a path length of 50mm. The tube threads onto the reducer, then the T-ring of the camera threads onto the other end of the tube."

My plate-solved focal lengths at a range of back-focus distances are graphed here. This implies a .63x reduction at ~120mm (2032mm x 0.63=1280mm).

Focal length at 85mm was 1420mm. The corner aberrations looked like this:

So it looks like either the available information is not reliable, or there is a lot of variation in these OTAs or correctors. I gave up (wasting too many clear nights) but I'd be happy for someone more capable than me to check my homework and comment on other factors like collimation.

Snap! I was imaging here on 7th and 8th April and got this result in my OSC stacks. Was convinced it was my calibration but couldn't explain it.

Fantastic! Love the level of detail.

I replied too soon! 🙂

Good to know that. I had assumed that if you want automation including an electronic rotator, you would also have to add a flip-flat-type flat panel so that flats could be taken automatically as part of the sequence. And those flip-flats ain't cheap!