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Thread: Aligning EQ mount and focusing DSLR

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    Default Aligning EQ mount and focusing DSLR



    Hi there. After enjoying the lunar eclipse, I am in the process of learning how to align my AVX mount (I have a Celestron 8" SCT). I have tried aligning it following the instructions using 2 star alignment and adding a third calibration star but afterwards the mount doesn't point to the correct objects. I live in Chile so I followed previous advice from fellow astrofans on where to point the mount to and adjusted the latitude on it. I believe that the fault may lie in that I am having trouble identifying stars. I wondered if using the Starry Night software can help with the alignment, but it requires aligning the mount first. Regarding my second question, I purchased a focal reducer for my Nikon D5600 (it worked great with the eclipse since it gave me a wider field of view), but I can't seem to find focus when using live view mode and thus I am unable to take pictures (also, there will be star trails if the mount isn't tracking). Any advice is appreciated.

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    Default Re: Aligning EQ mount and focusing DSLR

    Very difficult to tell just exactly what the problem might be. Even more difficult for me since I am a Northern Hemisphere person and don't know the Southern skies (I'd really like to see them some day).

    Getting a rough alignment using a compass and approximate elevation and then using the ASPA routine should work for you. It might take several iterations to get it really nailed down.

    Do remember that there is a very significant difference between doing a polar alignment of the mount vs. doing an alignment with the stars. In other words, you use one technique to align your mount's RA axis with the South Pole and use a different technique/routine to develop a model in the mount's computer brain for finding a target in the sky (orienting/modeling for GoTo).

    Personally, I no longer use the ASPA routine. It takes me too long and I just generally don't like it. I got the QHY Pole Master and it made things a whole lot better for polar alignment.

    After I have the polar alignment done I then do the calibration/alignment with the various stars and let the model be built for the GoTo function.


    One other thing? A lot of the time much of the confusion with these mounts is getting the time right. Where I live we deal with "Daylight Saving Time" and things like that. If you aren't very careful you can get the time entered wrong and end up with all kinds of trouble getting the GoTo function working properly. You want/need to be absolutely sure you are getting that right or you will deal with a lot of frustration.
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    Default Re: Aligning EQ mount and focusing DSLR

    I think ole cus has your problem pegged. First polar align your mount then align your mount to the stars.

    Your description of your difficulties brings back memories of the frustration I once had when I first started using my first German equatorial mount. While I knew that the mount must be polar aligned I did not know that you used the mount's alt/azimuth adjustments to align the mountand was moving the mount in DEC and RA. The result was that some nights when I accidentally set the home position nearly aligned to the celestial pole every thing worked as it should. Other nights produced gotos that were off with a consistent error.

    When you polar align your mount don't move the mount in RA and DEC, use the latitude adjustment and azimuth adjustment knobs.
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    Default Re: Aligning EQ mount and focusing DSLR

    Regarding your focus issue using live view. Keep in mind that with a SCT you can easily pass through focus and not realize it. Go slow, very slow.

    For a live view focus one method NOT using a mask is using an eyepiece goto the object you want to image, Center then synchronize with the object, then goto a nearby BRIGHT star, the brighter the better. Center and focus on the bright star, then carefully attach your camera. Focus first through the view finder then on your live view screen with no magnification. Finially focus at maximum magnification. At focus the star will be a small white dot .Once you focus do a goto back to the object you want to image.

    Note: If the star you selected for focusing is not bright enough it may not be visible on your live view screen.
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    Default Re: Aligning EQ mount and focusing DSLR

    Is the Celestron StarSense a good option for me, since polar alignment down here is so difficult? Also, will the SkySync GPS be useful as well?

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    Default Re: Aligning EQ mount and focusing DSLR

    The GPS only input local time and coordinates so not really worth the money in my opinion.
    I have not used the Starsense so cannot help you there.
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    Default Re: Aligning EQ mount and focusing DSLR

    Ole is right in that you have to align the mount to the polar axis before you do a star alignment.

    While most mounts have some built-in feature that helps you achieve a polar alignment (in addition to a star alignment), the accuracy usually isn’t as good as some other methods. A QHYCCD PoleMaster is awesome (most everyone I know who does astrophotography *and* who does not have a permanent mount/observatory ... uses the PoleMaster (I do know a few people who don’t). It really simplifies life because it achieves an amazingly accurate alignment in just a few minutes.

    But I suspect you’ll have more issues with that 8” SCT on an AVX mount.

    The lower the focal length of the scope, the more forgiving it is about tracking accuracy. If you were to just put a camera and ordinary camera lens on the AVX (no telescope) then a reasonably decent polar alignment would give you great results.

    But as you increase the focal length of the scope, the tiniest tracking errors become noticeable. An you have 8” SCT (that’s a 2000mm focal length). You will likely find that in addition to everything you have ... you’re going to need an auto-guider.

    The auto-guider is a 2nd camera (such as a ZWO ASI120MM-S ... but there are lots of choices) and either (a) a separate guide scope *or* (b) an off-axis guide adapter (there’s also something called an “on-axis guide adapter” but those are expensive).

    If you used a 2nd scope (a guide scope) this should be something where the focal length of the guide scope is a reasonably decent fraction of your main imaging scope (like 1/3rd of it’s focal length). In other words with a 2000mm focal length main imaging scope, it would be nice to have a guide scope with a focal length around 600-700mm focal length). This creates two new problems which are (1) how to mount it (piggy back vs. side-by-side mount adapter) and (2) that extra weight creates more stress on the AVX mount and some flex Ure.

    If you use an off-axis guide (OAG) adapter, the OAG has a tiny little “pick off” mirror to steal some light off the edge of the field and send it to the guide camera. But this means the guide camera’s sensor has to be shined to be *precisely* the same focus distance (basically you measure the distance from the pick-off mirror to the main imaging camera’s sensor... and shim the off-axis camera so that it’s sensor is the same distance from the pick-off mirror (except that’s at a 90 angle). Also ... any filters attached in front of the OAG will end up filtering both cameras (don’t use an Ha filter ... the guide camera will struggle to see stars.). But at least the OAG doesn’t add too much extra weight (much less than a guide-scope).

    If imaging with the 8” SCT on a AVX mount is a struggle, consider switching to a shorter focal length refractory (say ... 500mm focal length). For example... Explore Scientific makes some 80mm f/6 APO triplet refractors (that’s 480mm focal length). That focal length (being 1/4 of what you’re using now) will be much easier to get good tracking and round stars. It weighs in at just over 1/3rd of what your 8” SCT optical tube weighs.
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    Default Re: Aligning EQ mount and focusing DSLR

    The StarSense should be able to help you get your mount's model of the sky set up - and therefore your GoTos will be improved.

    If you go to the StarSense manual: https://s3.amazonaws.com/celestron-s...bruary2016.pdf and look at page 16 you'll see what they want/need you to do for polar alignment. It looks to me like it is pretty similar to the ASPA built into the AVX. The advantage is that the autoalign sets things up so that you don't necessarily have to have great knowledge of the stars in your sky.

    So yes, I think you would find the StarSense to be helpful but whether you will find it to be worth the expense and fiddling with it I cannot guess. Early on there were significant firmware/software issues but I've not been hearing/reading of many problems recently. It appears to now be a pretty mature technology with users who are generally pretty happy.
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    Default Re: Aligning EQ mount and focusing DSLR

    Well I do have an Astromaster 70 that my grandpa loaned me. I know it's not the best quality, but would it help me learn the ropes of aligning?
    I read the page you mentioned Olecuss. Perhaps I also need to know how to adjust the screws on the mount besides the elevation ones. I believe I will order the Star Sense in a while, and eventually will purchase an APO. In the meantime, I will focus on planetary observation, since the SCT is better for it given the large apertura size and focal ratio. Also, planetary alignment apparently is easier. I think… maybe… ok I have no clue.

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    Default Re: Aligning EQ mount and focusing DSLR

    There is nothing at all wrong with working/learning/observing with an AstroMaster. Depending on the mount you use with it, it may or may not help you with learning to do polar alignment.

    But I don't know how to do a "planetary alignment" with a GEM like the AVX. So far as I know, you are either polar aligned or you are not polar aligned. You do get sidereal, solar, and lunar tracking rates but so far as I know you still do a polar alignment no matter the rate you plan to use.

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