wimvb

Hasselblad nowadays also have a 44 x 33 mm sensor, but with 50 MP resolution. The price is half that of the new ASI. I sold my Hassie years ago, and used the funds to get into astrophotography.

I guess that your formula is derived for a Newtonian, where the mirror is the aperture stop. In a MN I believe the meniscus is the aperture stop. Simply put, if you can see all three mirror clips in the Cheshire eyepiece, use the mirror. Otherwise, use the baffles or meniscus. I have my formula from Suyter’s book Star Testing, which uses the simplified formula Offset = H / 4F^2 = H/112 for the 190MN A guesstimate of H is 230mm, giving an offset of about 2 mm, give or take a few 0.1mm

@coenie777, where did you get the 3.7 mm offset for this scope? If I use the formula given by Suyter, I get close to 2mm. And I also have an uneven illumination, but this is easily corrected with flats.

Hasselblads (at least the classic 500 model with 60x60 size) were never good for AP anyway, they didn't have a shutter. That was always built into the lens.

I don't have a proper drawing app on my tablet, therefore low tech rather than high tech. If you lower the secondary mirror (green), you also move the reflected light cone down, and it won't be centered under the focuser anymore (bottom green). You could of course lower the focuser as well, but there's little point in doing that. You would also need a larger secondary to cover the wider light cone. The position of the focuser determines the position of the secondary. If you have a large enough secondary mirror, you can slide it along the plane of its reflecting surface without upsetting collimation or the Maksutov criterion. The collimation view will look asymmetric. If you slide the secondary along the plane of its reflective surface, you move it both down (or up) and away from (or towards) the focuser. But, in a telescope, the physical centre of the secondary is at a fixed distance from the optical axis. So, unless you remove it from its stalk and glue it in another position, you can't move the secondary up or down without also moving the light cone up or down. In an optimised configuration, the secondary mirror is only slightly larger than the reflection of the primary mirror. If it would be much larger, it would obstruct the incoming light too much and you would lose contrast. If it would be smaller, you wouldn't use the scope to its full potential. Essentially the aperture would decrease, making the scope slower. In an imaging system, the aperture is determined by the element that restricts the light cone most, not necessarily the front opening of the scope. In a Newtonian telescope, this is always the primary mirror. It should never be the secondary. In an optimised aystem, there is a very narrow dark ring between the reflection of the primary mirror in the secondary, and the edge of the secondary. Btw, if you move the secondary mirror down and tilt it to "recenter", you will also need to tilt the focuser to achieve something which resembles proper collimation. If you don't, it will look like you have unintentional tilt in the focuser.

The focal plane of a telescope is independent of the camera used, and many optical correctors have a back distance to the focal plane of approximately 55 mm. But the flange to sensor distance of most dslr cameras is about 45 mm, while for astrocameras this is often less than 20 mm. Adapters for dslr cameras are typically 10 mm (+ 45mm = 55 mm). Astrocameras need spacers between them and any correcting optics, and the distance you need is critical. Nothing is ever easy in this hobby. Btw, you can’t wing it as far as focusing is concerned. It needs to be spot on, so prepare to invest in software.

More and more amateurs nowadays pool resources for large scopes in remote areas. These will be the main target group for this model, I’d think. Also, sites where you can hire imaging times would be potential customers. Btw, 44*33 mm strictly isn’t medium format. Medium format roll film cameras were 60*60 mm (Hasselblad) or 60*45 mm (Pentax). This sensor is still half the size of a Pentax 645. Otoh, not many focusers could support such a camera, weight wise.

Not many scopes can support a 55 mm diagonal. And any filters worth having will cost another fortune

Thanks! You are correct of course. Where on the tube you put the focuser is irrelevant, because the only task of the secondary is to fold the light cone 90 degrees. It also needs to bring the focal plane at a sensible distance from the tube’s surface. But without any adjustments you have zero tolerance in the fabrication process. So, screws to the rescue. I am writing this on a bus on my iPhone without a proper keyboard, and can’t elaborate much more atm, but during the weekend I’ll try to write in more detail. The short version is that to get even illumination you need to slide the secondary along its reflecting surface once it is at 45 degrees opposite the focuser. But you can’t do this with a fixed distance between the secondary center and the cone’s axis (lateral offset).

Maksutov telescopes need to have a fixed distance between the meniscus and the primary mirror. Also, meniscus and primary must have the same optical axis. In the original Maksutov design, meniscus and mirror are the only optical image forming elements. The image plane /focal plane is on axis. A Maksutov Newtonian has a secondary mirror to fold the light path off to one side in order to accomodate for a focuser. Where that mirror sits in the optical path is not critical, but the position of the focuser determines the position of the secondary. Moving the secondary along its reflecting surface is always possible without affecting alignment.

@Shibby you can do a star test with camera. Just defocus and look at live view / streaming. That is what I usually do. Make sure that the star is on axis, as all other stars radially outwards will look out of collimation. Also, if you defocus the star too much, you won't get the same detail. Try to defocus just enough so that you can see a donut, then zoom in on the image to get a better view. The defocused stars in my off axis guider allways look horrible, like bananas. This is because the oag prism and stem are not aligned perfectly with the optical axis of the telescope, and the stars are off axis. But once focused, the stars look nice and round. Yesterday, I recollimated my 190MN, more or less from scratch. I got good collimation with a variation of the recipe I described earlier. 1. centering the marker on the secondary with the help of hte crosshairs on a cheshire (using OCAL would also work). The focus tube and cheshire need to be pushed in just so much that you can see both the crosshairs and the marker. Normally, this step shouldn't be necessary, because any adjustments you can make on the secondary, are rotations and tilts around this marker. Unless the secondary is too far inwards or outwards, any secondary mirror rotation or tilt, won't change the position of the secondary marker by much. 2. using a barlowed laser collimator, get the shadow of the marker on the secondary to lign up with the marker on the primary. This is where you adjust the secondary. My barlowed laser collimator is just a cheap but collimated laser collimator inserted in a SW barlow. 3. get the reflected marker of the primary concentric on the target of the laser collimator. This is done by adjusting the primary mirror. Again, OCAL would work in a similar fashion. A star test with my astro camera showed excellent alignment. During the collimation, I didn't bother with having anything concentric, but once done, all that needed be concentric, was.

During summer holiday I dust off my 22” spherical kit. It has an integrated tripod with wheels on two of its legs. I exclusively use it to view the coalsack. An ideal instrument for star parties. Brand: Weber

Remember the double slit experiment from school? (It also works with one narrow slit.) The slits are vertical, but the diffraction is horizontal.

Cmos astro cameras are more sensitive than SLR. You also mention that you are interested in a cooled camera. This will make the calibration process easier, especially since the ASI294 has amp glow that requires careful calibration. If I were you, I would go for a newer generation camera that doesn't have amp glow. Bortle 5 is not that light polluted, but if you are concerned that it may be a problem, you should look into mono imaging. RGB filter are generally designed to suppress conventional sources of light pollution, sodium and mercury lights. If I were in the market for a new camera, I would probably add an osc to my collection (Bortle 4 skies). But I already have mono cameras.

So far, I haven't sent any expensive astronomy products by mail or courier, but last year, an item that I had ordered from TS was lost as soon as the parcel was handed over by the international courier to PostNord (Swedish postal service, aka PostMord, mail murder). Luckily I got a new item from TS. I think that it may pay off to put an Apple Airtag in any pacakge that contains anything of value. The Airtag could then be sent back, or simply written off.

Btw, do any test on stars with short exposures and near the celestial pole, so you can neglect trailing.

The more I think of it, the more confusing it gets. I tried to find a diagram that shows the setup. https://skyandtelescope.org/astronomy-equipment/offsetting-your-secondary-mirror/ All the discussions (including the links to CN which I posted earlier) sooner or later mix ordinary Newtonian collimation with Mak-Newt collimation. It's there where it gets confusing. Here's my own reasoning (which may very well be completely wrong). The corrector or meniscus in a Mak-Newt is fixed in place and must be at a fixed distance from the primary mirror. Also, the center line (optical axis) of both the meniscus and the primary mirror must coincide. This essenially fixes the primary mirror. (Hence the o-rings in stead of springs for adjusting the primary with regards to the cell. IF there were no mechanical tolerances, the primary could be locked in place.) The secondary mirror sits at 45 degrees angle to the optical axis with what the S&T article calls fully offset collimation. If you move the secondary up or down the tube, you also need to move it closer to or away from the focuser. But this can't be done in a Mak-Newt. In a conventional Newtonian you can collimate and center everything by combining a fully offset collimation with a partially offset collimation. This is a combination of diagrams B and C in the S&T article. But for this to work, you need to slightly tilt the primary, and tilt the secondary an equal amount from its 45 degrees position. Tilting the primary messes up the Maksutov configuration. Hence the number 1 rule for Mak-Newt collimation: DON'T MOVE THE SECONDARY UP OR DOWN THE TUBE. In a Maksutov design, all focusing optical surfaces are spherical, so a very small amount of primary tilt with respect to the meniscus may not be visible in collimation, which is done at the optical axis. But it will most likely show up off axis as coma or other aberration. If I'm correct, the view down the focuser tube of a collimated Mak-Newt should look like that from a conventional newtonian with fully offset collimation. AfaIk, the primary mirror reflection and its center marker should be concentric with the focuser edge. The description earlier in this thread of how I collimate my Mak-Newt should also hold; pull the primary down to its cell. Adjust the tilt and rotation of the secondary with a well collimated laser and finally adjust the primary to get the laser beam back onto the collimators bullseye.

I feel with you. I’ve been close to throwing in the towel several times. Fortunately the engineer in me wouldn’t give up. With high end gear, this shouldn’t be an issue. But it seems that regardless of how much we throw in the money pit, there will be frustrating moments.

Wow, that's fast. I've driven that stretch a few times (well, almost that stretch), but don't think I 've ever come close to keeping almost 100 km/h for the average. 😉 😉 Great write up, btw. As @tomato already hinted at, my concern with Mesu (company/product) would be, what happens when he (the person) decides to call it a day and retire from his business? Even if he sells the company and designs, that won't mean much without the expertise behind it all. So far it seems that Mesu mounts are very durable, but what if a mount needs service after Lucas retirement? The mounts are of excellent quality, as shown by their track record. But it's not only the product that's important, but the entire supply chain during the product's lifetime. Just wondering...

Regarding centring, read Vic Menard's (he's the one who literally wrote the book on collimation) reply in the above CN link, msg #19. Essentially, focuser tube, outer edge of secondary, and reflection of primary should be centered. Reflection of secondary is not centered.

A lot has been written about collimating the Mak-Newt. The consensus is that the secondary offset is factory preset, and it shouldn't be moved up or down the tube. Also, the corrector to primary mirror distance is critical, and should be kept as it is. (The primary mirror has double o-rings on each collimation screw, where normal newtonians have springs. This is because you shouldn't be able to push the primary up the tube, only tilt it.) Unlike an ordinary Newtonian, the optical axis of the corrector (= tube axis) and the optical axis of the primary have to coincide, and the focuser must be at 90 degrees. (In an ordinary Newtonian you can have perfect collimation with everything at an angle to the tube axis.) https://www.cloudynights.com/topic/701041-before-i-get-crazy-mak-new-collimation/ https://www.iceinspace.com.au/forum/showthread.php?t=140193 I don't have an OCAL, and only use a (barlowed) laser collimator to collimate my 190MN. To get a baseline, I pull the primary all the way back to its support, and start from there. Because the primary is all the way back, I only need to use two screws to adjust it. The final test is always a star test, with a star only slightly out of focus.

The Omegon version probably works just as fine as a possible ZWO camera will, at a fraction of the price. Drivers shouldn't be a problem, unless you're on a ZWO leash (ie, use an ASIAIR).

Assuming good polar alignment, you could take a single exposure long enough to cover one worm period, while slewing the mount in DEC at less than or equal to sidereal rate. The star trail not only shows p2p periodic error, but also its form.

Like @ONIKKINEN no astrodarkness here either. From 31 July on we have at least nautical darkness again. Narrowband Ha will be doable then.

Efw's should be light tight, unlike manual wheels which have an openi g to turn the wheel. I find it strange that th leak is external (spacer) yet only affects a few positions. I would expect an external leak to affect all filter positions. So, you need to find out what is special about position 2. Have you ever dropped or bumped the fw, causing something to bend or go out of alignment? Are ther any reflecting spots (paint worn off?) near position 2? I would probably disassemble the optical train and inspect each part. What you also can do is put the camera in streaming mode, and look at the stream while changing filter positions. If you do the streaming in a dark room, you can move a dimmed light around the setup to find the exact location of the leak. Third, you can replace the spacer (never mind which length you replace it with, this is only for testing) and check if it is the spacer that is the culprit. Although, I doubt it will be because, as I wrote, this should affect all filter positions. Does duct tape completely remove the light leak, or just make it less obvious? You could try black electrical tape, which may keep more light out. Of course it's always better to fix the cause of the problem.