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| Some people have said that a $30 apertura 0.5x reducer will just be bad. Is this correct? If it is, what makes it bad? |
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Hi, A reducer causes various aberrations, especially chromatic aberrations and field curvature. Also the reducer makes the image circle smaller which will cause noticeable vignetting unless your sensor is very small. small. The more expensive reducers that you see for refractors, reflectors and certain catadioptrics are calculated for a specific telescope (or a specific range of telescopes with the same basic design), made from special glasses and include extra corrective elements to keep the image free from distortions. Also, they generally settle for a less drastic reduction. It will not necessarily look horribly bad (especially at the center or with a small sensor), just don't expect it to look as good as the native image from the Mak or from an instrument that is natively at half the focal length. It is a tradeoff. |
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Some people have said that a $30 apertura 0.5x reducer will just be bad. Is this correct? If it is, what makes it bad? That won’t work with a 127 mak. Ive tried. I have a 127 maksutov cassegrain though that I have used extensively for deep sky imaging though, with a reducer. Most of the images I’ve posted on this forum were taken with that. I once had to figure all of this out so I can tell you exactly how to reduce your 127 mak with a 0.63 reducer that works. I took my native F15 Meade Mak down to an F9 this way & have done tons of imaging with it. Here’s what I did. It was a bit of a mystery quest finding all the right pieces to do so successfully though as there really aren’t many maksutov specific reducers out there. First off, unlike a Schmidt cassegrain, a maksutov already corrects & flattens the image with its internal optics. One of the key design differences between a maksutov & Schmidt is that the secondary in a maksutov is also a corrector. So...what this means is that very few reducers that are designed for a Schmidt will work for a mak because Schmidt reducers also flatten the field. So a standard Celestron 0.63 reducer they sell for their standard Schmidt-Cassegrains (something like a C8, not their edge HD line), will not work with a mak because it also is a field flattener. You don’t want this. Therefore for a maksutov cassegrain you need a reducer that is a reducer ONLY with no correction. I have found exactly 1 of those out there, this Antares unit. OPT still has these, but it has been discontinued by Antares. So if you want one get it now. If OPT is out of stock they may be out for good since this is no longer made, but check astromart. If OPT says “more on the way in 14-28 days” never take this at face value. That is their default message when they’re out of something & is almost never the actual lead time. In the case of this reducer if they are at zero they’ll never get more.. I have seen several of these Antares 0.63 reducers for sale on astromart within the last week though, so that’s your best bet. https://optcorp.com/...t-focal-reducer The second issue you’ll run into in trying to use this with a mak is getting an adapter that can handle the SCT thread on the reducer & connect to the mak draw tube. There is no consistent standard for thread size on a maksutov cassegrain. Many, including mine have a 1.375” opening. So in my case I used this baader adapter to fit the reducer to my telescope. The adapter also has a slot within for a 1.25” filter that can be inserted inside with still plenty of room for it to fit on reducer & telescope. I bought that from Agena https://agenaastro.c...xstar4-c90.html Finally, from there you will have to figure out the correct back focus from the end of the reducer to your camera sensor. This was a project in itself because the reducer came with zero documentation at all & there is no published backfocus spec online from Antares. I discovered through trial and error that the correct back focus needed is 105mm. You will see some different numbers thrown around if you start digging on different threads here (82 and 85mm have been thrown out there. These numbers are wrong.) I can promise that 105mm is the correct distance. I had to learn this the hard way. So...to achieve this 105mm back focus & connect the SCT thread from the reducer you can use this celestron 50mm adapter, which is perfect if you are using a canon DSLR. From the front edge of the t-ring to the sensor on a canon is 55mm, so a 50mm spacer puts you right at 105mm back focus. The celestron 93633-A is that adapter. https://www.amazon.c...a/dp/B07TMD2CW8 If you aren’t using a canon DSLR you’ll have to get to that 105mm a different way of course. I now have switched to a QHY268C & have figured out a different configuration to connect the camera. I found this little YouTube video that addresses a practical way to mount a camera to SCT thread that also allows for you to attach a 2” filter into the chain after the reducer without the need for the filter drawer. This is what I do now. This is most flexible because you can adjust backfocus by adding/subtracting M48 spacer rings. The 105mm backfocus I gave has some play. There is a range that will work. https://youtu.be/KroQe3Pu7Ic All of the above info took a lot of digging around to figure out when I did it for myself since info on reducing a mak-cas is HARD TO FIND. So I hope this info saves someone else a lot of trouble and time. |
