going prime focal

[silv]

I am thinking about going prime focal… (how does that sound? :lol:)
8" newtonian, 1000mm focal length, f/5 and my Sony Nex-5N.

This afternoon, I pointed my Sony Nex-5N with the 18mm lens into the focuser. At a height of about 10-15cm above the telescope tube, the image of the tree was visible for the camera and focusing with the focusing ring on the cam was possible. Mind, I had to hold the cam at a certain angle so that the secondary mirror was not filling the most of the view through the barrel.

Any closer to the focuser and the image got more and more blurry until - when the lens almost touched the focuser - apart from the mirrored focuser, there was only green color left with no chance to get that more into focus.

Then I took the lens off - as would be the case at prime focus with t-adapter and ring thingies.
My camera then only shot an even colored picture - depending on the brightness of the room: blueish green in my room and whitish when pointing outside into the garden. A pic from close up to the focuser also was bluish green, same as the photo of the room in general.


Is all that normal? :question:

How do you focus with your camera once connected with t-ring and t-adaptor - and the lens is off?
The Sony Nex-5N has a live display and it is pretty much showing what you'll get in the photo; it's also taking ISO, Aperture and shutter speed into consideration.
Should anyone be in doubt: the Sony is used in prime focus as can be seen here:
http://sonyalphanex.blogspot.co.nz/2012/02/sony-nex-5-with-celestron-c8-sgt.html

[silv]

the green view with the lens on and close up to the focuser:
that must be a case of focal point alteration:
either by moving the primary mirror (eeek!) or by getting a device that somehow shifts that focal point mechanically/optically/virtually to the observed 10-15cm above the tube?
and to what cost? I mean - cost in light an weight?

but I wouldn't HAVE the lens on once I connected the naked camera. So how would one go and find out the correct focal point for a lens-less camera?

Any input - just some keywords, even, would be very helpful! Thanks :)

[arifmshaikh]

You can focus same way you focus by putting eyepiece. You may be able to bring the camera focus during daytime, but you will need more in focus.

I did my 200mm f/4 Newtonian by moving primary mirror, but then you will need extension tube for normal observation.

[silv]

ah! I had come across that term "extension tube" but only now I understand what it is for. thank you :)

hm. that means I would use the focuser wheels. okay. I understand.

i don't really want to move the primary mirror... was it difficult?

[silv]

found this article and am reading it right now...
http://www.iceinspace.com.au/forum/showthread.php?t=55226

[arifmshaikh]

It is not difficult to move primary. First you test your setup on star and see if it comes to focus or not. I have skywatcher 200mm f/5 which comes with extension tube, so I believe I can get the focus with prime focus(still need to try).

I used long screws and spring bought from bunnings to achieve focus the my old f/4. The other alternative is cut the tube.

[silv]

bugger - so many good questions there and almost no answers...

read this (http://www.iceinspace.com.au/63-441-0-0-1-0.html) article - and can not - will not - must not - move the primary. Cutting the tube? Never!
But it mentions the other gear to achieve something similar:
low profile focuser and Coma corrector.
Intriguing: the focus point is closer to the secondary - contrary to my afternoon experiment.

Arif, you solved it with springs and long screws? Did you follow any internet article when doing it?


magical optics ...

[arifmshaikh]

[QUOTE=silv;876213]bugger - so many good questions there and almost no answers...

read this (http://www.iceinspace.com.au/63-441-0-0-1-0.html) article - and can not - will not - must not - move the primary. Cutting the tube? Never!
But it mentions the other gear to achieve something similar:
low profile focuser and Coma corrector.
Intriguing: the focus point is closer to the secondary - contrary to my afternoon experiment.

Arif, you solved it with springs and long screws? Did you follow any internet article when doing it?


magical optics ...[/QUOTE


I read the following review for my modification http://www.cloudynights.com/item.php?item_id=1677

If need to calculate how much back focus you need and then church the low profile focused height. I did mine because I wasn't sure the low profile focuser will solve this profile.

[silv]

cheers arif!
your input was very helpful and I feel I can get it done, somehow, now.

this was an eye opener, too.

[silv]

one last question:
if it turns out that I can not get focus with the lens off (just a feeling),
how do I then subtract the 18mm lens from the measured length of the focal path to get the focal point of the assumed lens-off situation?

[arifmshaikh]

The simple method is find the difference of focus. Use any eyepiece and focus on object 100/200 meter and mark on the focus tube. Now use the same eyepiece and focus on star and mark on the focus tube. Now you have difference of let say 20mm. Now mount your camera on telescope bring same object 100/200 meter away to focus. You have to take focuser all the way down to achieve focus. If get the focus and you still have few mm to travel in, minus this few mm from the focusing difference that you get from the eyepiece, whatever difference you get that much you have to move your primary.

Even if you can't get focus, then move the primary with existing collimating screw, this is how I did to find the difference. I had the same GSO ota that was mentioned in the review.

[ZeroID]

Silv, I had to add 25mm to my mirror supports to bring it to focus on the DSLR at prime. About the additional distance of the CCD sensor to the EP as opposed to where your eye would be.
I use an extender for a few EPs but as I am heading into Astrophotog that will be a minor issue.
I just added three equal distance 25 mm spacers I made up on the lathe, longer adjustment bolts and shifted the mirror plane up without cutting or major alterations to the OTA. The mirror got a wash at the same time.

[Shiraz]

should be a really good scope/camera combination.

at prime focus, you will use the scope as the lens for the camera, so you will need to run the camera in manual, and set all parameters by hand. Focusing will be manual by way of the scope focuser.

Its not clear how much of this you have already done, but to check if you can get focus, focus the scope through an eyepiece at something a long way distant (you need something a few km away to keep this test simple) from inside a darkened house (through an open door/window, not through glass). Measure the distance between the top of the fixed part of the focuser and the top surface of the eyepiece adapter. Then take out the 1.25 eyepiece adapter and wind the focuser in as far as possible - measure the distance from the top of the fixed part of the focuser to the top surface of the moving part. Then hold the camera (without lens) up hard against the end of the focuser tube and adjust the focuser outwards. If you can get a good image, you may be in with a chance of getting it to work without any scope modifications. Measure how far out you have wound the focuser to get focus and if that distance is greater than the height of the camera adapter, you will be OK.

If you cannot get focus, the CCD in the camera is too far away from the front of the camera and you may need to move the main scope mirror up the tube a bit to compensate - longer bolts, spacers and springs as Brent suggests if you don't want to modify the tube, but be very careful that the longer bolts cannot possibly touch the mirror. A lower profile focuser might also give you enough extra focus, without moving the mirror, if you can get get to focus, but don't have enough focuser travel to fit in the adapter. With an f5 system, you will probably need an MPCC to reduce coma at the edges of the image - really depends how fussy you are. The MPCC will also help by adding 10mm extra back focus, but it adds extra problems of its own (getting the right spacing for your camera). To make the best decision, you really need some measure of how much extra focus your system needs. If you cant get it in focus in the above test, post the focuser distances you measured and someone will help you work it out. Would also be helpful to know the distance from the front face of the lens mounting ring (lens off) to the CCD chip (should be visible looking into the camera from the lens mounting) - just guess by eye, don't put anything inside the camera body.

If you want some idea of what you will get at prime focus, put in a 15-20mm eyepiece, fix the 18mm lens on the camera (set it at infinity in manual focus mode) and hold the camera+lens in front of the eyepiece (in the darkened room looking at something distant through the door/window as before). You should be able to focus an image using the scope focuser - the eyepiece and camera lens act as transfer optics to get the image formed by the scope onto the CCD. This method puts lots of glass components in the imaging train, so it is not the best way to go, but it will at least show you what you can expect to see when you get it going in prime focus.

[silv]

:bashcomp: oh, sooo angry! grrrrrrr!

What am I missing???

in order to find a focal point for the lens-less camera in the telescope I would have to be able to find any focal point anywhere, right?

So I take the lens off, outside (where it's not raining atm ;)) I aim at my finger at 10cm distance (or closer or further) from the chip:
all I see in the life view is whitish light with maybe a shadow of darker white caused by the finger.
I shoot the pic: same.

There is no option to focus without lens.
There is no option to set AF to "infinity" - a term I have read often, used by people with Point-And-Shoot, I think. While mine is no point-and-shoot - lenses are interchangable but it doesn't have mirrors.

What are the camera settings I need to use without the lens to get focus?
Without that, I can not measure the focal point distance from the secondary - hence can not decide for a focuser.
Can't decide for a possible primary mirror move, either.

Grrrrr!

(I don't have any t-mount acessories, yet, figuring they will be determined by the focuser I might eventually buy.)

[silv]

Arif, Zero - thank you very much for your help. It will be useful in the next stage of my learning...

[Shiraz]

No Silv, you don't get an image without a lens - the lens takes the jumbled light from a scene and makes an image of that scene on the sensor chip of the camera. Without a lens all you get is the jumbled up light. At prime focus, the scope is the "lens" and it forms the image on the camera sensor - you don't need any other lens. The camera plays no part in focusing anymore, since it does not control the scope - you focus by hand with the scope focuser.

to set the camera lens to infinity when doing the demo suggested in earlier post, use "manual" focus mode, not AF, and physically move the focus ring on the lens to the infinity mark.

When using the camera with the scope, you should only need to set ISO and exposure time in "manual" exposure mode (eg ISO200 and shutter around 1/500 will probably give you something recognisable in daylight). Aperture is determined by the f5 scope, so you can ignore that - focus should be set to "manual" and also ignored.

[silv]

shiraz, that's odd.
your post from this morning only shows up now for me. ....
hadn't seen it when I posted my previous one.
will read this now. cheers!!

[Shiraz]

I might have been editing it when you looked maybe. anyway, let's know how you get on - I tend to be a bit longwinded

[silv]

that sentence has had a motivating effect. cheers shiraz.

the distance from the top of the lens mount (lens off) to camera chip surface is ~1.8cm, maybe less .

*

the e-mount lens I have doesn't have an infinity focus marker.
the camera focus settings don't have an "infinity" setting.

But I understand that this is of no consequence for prime focus. Thank you for clearing that up!

I will drive somewhere and test from inside the car.

I understand. I can do that.

:jump:

[silv]

I suffer from that infliction, too. ;)

But in this case your winding was necessary and very very helpful.

[silv]

adding pics of camera - with lens and no lens.

[dannat]

CNC parts supply in the US make a t minus adapter for your camera

[silv]

yeah, but the T thingies will be determined by the new focuser. so I need to figure that one out, first.
cheers daniel!

[silv]

distance to test object: ~ 1.5km

hight of static part of focuser from top of mounting plate: 2.4cm

camera at prime focus:
Distance top of static part of focuser to top of moving part: 4.4cm

==> 6.8 cm from mounting plate to focal point

(40mm K. eye piece focusing same object:
Distance top of static part of focuser to top of moving part: 3.3cm
why was this measurement necessary?)

the image quality was really poor. washed out, blurry, dark.
I hope that was caused by high humidity, warmer tube than outside air and my awkward acrobatics on the back seat of the car ...

will have to repeat test on stars with scope properly mounted and cooled.

but view through 40mm K was good.
the FOV was much bigger through the eyepiece, too. ... must keep that in mind that the camera produces such a tiny field!



the 1st photo was taken with same settings as the prime focal one: ISO 200, 1/250secs - it shows the object on the distant hill at the horizon.
2nd photo: prime focus
3rd: prime focus cropped and lightened

[silv]

a T-minus adaptor (http://www.telescopeadapters.com/index.htm?TMINUS.htm), as Daniel has suggested, is supposed to be "an inch shorter" than usual t-ring-t-adapter solutions. that's how far the specification re length goes ...

I hope that this one part does not require a t-ring but screws directly into the lens mount and fits into focuser barrel?... I hope. daniel? did you buy this part?

it's a 2" solution; my current rack&pinion focuser is 1.25".

now I need to find a 2" focuser "low profile" which is within the 6.8cm range of the focal point and still allows for the "1 inch shorter than usual t-minus-adaptor".

or move the mirror....

is that correct?

[silv]

Jesus, *huge sigh* in pre-WWW-times, I would never have been able to get this far - let alone get to the finish line, some day.

How did people learn about all this new stuff without google and IIS?

[gbeal]

Silv,
What you need is someone standing next to you that has been through all this.
If you get 100% stuck, contact me via PM, and somehow we can meet up. Failing that, try Andrew Buckingham at the Auckland StarDome, I'm sure he will be able to assist. He also is likely to have some of the bits you may need.
Once you get it working you will realize how simple it really is. I successfully used a Nex5 on my scopes, now use a Fuji, same principle though.
Gary

[silv]

:lol:

I wouldn't want to be that someone standing next to me ...

And I wouldn't want to put that kind of load onto one single person's shoulders, either.

I am a complete noob in ALL aspects; optics, mechanics, using tools, DSLR photography, astronomy ... did I miss anything?

I get impatient now and feel the pressure... because very soon, I will have to start looking for a new job and then go to work all day. I won't have the time nor the energy, anymore, to fiddle and figure and find out about things - like I did for the past 3 months.

And I am not there, yet. Simply not there, yet.

Sorry for the rant. :o

[silv]

Maybe, I will take you up on the offer, some day. And maybe, I will contact Andrew. Thank you!
(I was hoping for star parties but they were all canceled since I joined the club. )

Ah well. It was fun up to now. Really good fun!
Gotta see to it that the dollar flow changes direction.


:hi:

[Shiraz]

images!! well done.

the prime focus image is washed out by haze and stray light getting in all over the place, but it doesn't look too bad at all considering how you took it. (stray light was the reason for suggesting that you image from inside a darkened room). Try enlarging the same portion of your first image and see how much better the scope is.

from your measurements, the image plane is a fair way out from the tube and you have 2cm to play with in the existing focuser. If it is only a 1.25 focuser, you will need to get a 2inch Crayford, and it looks like you probably have enough back focus to use a standard one without moving the mirror. I don't have my scopes where I am, so can't measure one up, but maybe someone else can help. The adapter that Daniel suggested looks ideal. Most of it will slide into a 2 inch focuser tube and only about the top 8mm of it (the knurled ring and the bit with the white dot) will be visible between the focuser and camera. You probably have more than 8mm of focus adjustment available, so this should work fine.

"why was this measurement necessary?" only needed if you had been unable to get to focus.

Suggest that you take Gary up on his very generous offer or see if someone from the club can help. Someone with experience could size up the situation in a few minutes and save you hours of frustration and potentially unsuitable purchases.

anyway, congrats on getting some images - your system works.

[silv]

when motivation is low, little sentences like this open the brain by brightening the mood :)

it looks as if tomorrow night there will be a cloud break - the dry kind. I will measure prime focus, again, on stars.
The focuser tube height will vary with the distance to the object to be focused on... hmm. only now, your test requirement of a few km distance makes click.

Shiraz, thank you for your help!!

[silv]

Re the tiny field of view on the tiny camera chip:
I noticed that by moving the camera on the focuser barrel, I got different parts of the whole image that was visible through the eye piece.

is there a device that would allow the camera position to be adjusted while mounted in prime focus? I mean, without having to move the whole telescope? or will the FOV be bigger once the camera is properly mounted?

if such a device exists, it must be somehow determined by the focuser model it will sit in. or rather, the focuser model will be determined by that device and the focal point of the t-mounted cam.

Ah... a Focal Reducer (http://www.opticstar-ccd.com/Run/AS/AS-Editorial.asp?p=0_10_19_1_6_200_30# focalReducers) enhances the field of view.

Hm, ... it works with glass. I can't afford good glass at this stage.


It might be possible to get a device which can move the camera while mounted.
I could then take several partial images of the whole sky covered by the secondary as seen through an eye piece - and stitch the images together, later on.

my way of googling this does not yield results.

Lunch now. Then job search.

[Shiraz]

the chip is actually a fairly big one as chips go.

as you slide the camera around you will get images from different parts of the focal plane produced by the mirror. Only the central bit is really good and you want to firmly fix your camera so that bit stays on your chip. When you collimate your scope you are positioning the primary mirror so that it puts the best bit of the image plane on the centre of the chip.

One of the reasons for using a scope is that it will give you high magnification so you can see fine detail (it also captures lots of light). Forget about focal reducers and image stitching for now - your combination will provide a good field of view for years worth of imaging.

You will probably not get any useful results on stars by holding the camera against the focuser - they are hard to focus on without a very steady setup and you will need to use exposure times of seconds rather than 1/250. Could try it on the moon though - you might be lucky and get a wobble free image and you can also measure the actual height of the focal plane. You should see the whole of the moon.

then you need to wait until you get a better focuser and a camera adapter before you can try serious imaging. Therin lies a whole new set of challenges.

[ZeroID]

Hahahaha , we've all gone through that phase at one stage or another Silv. It's all part of the big learning curve. Half the fun is solving the problems and learning the lessons I reckon. One of the reasons I love it anyway, I NEED a challenge to keep me focussed.
Hang in there and it will all come together. I can post a few pix of my prime setup and the components if it helps. You do need manual control.
I set mine for BULB and use a remote timer cable as the max is 30 secs without. Also means I don't have to touch anything to start the exposure.

[silv]

:rofl::jump: :rofl:


:thanks:


:rofl::jump: :rofl:

[silv]

good test!
I felt and saw what happens with a bad focuser.
the words "feather" and "touch" were on the tip of my tongue ...

I also found that I will greatly benefit from a pure visual observation phase. I haven't done that at all, yet. Only for star aligning - and apart from that I captured piggy back photos.

But it will help me find my way around with the smaller field of view in the mounted camera.
With a better focuser, focusing itself will be easy in 4x zoom of the live view display.

I am really happy. Yay! Thank you all and thank you Shiraz!

[silv]

the star images tonight were all wobbly in the same pattern. I assume that was caused by the shutter on the ingeniously stable rubber band mount.

they also showed some coned and some circled shadows which are not to be explained by that wobble.
that could be just the normal "coning" effect I read about but it could also be something else.

I read Shira'z thread (http://www.iceinspace.com.au/forum/showthread.php?t=82230)about a DIY additional collimation tool and checked my super duper collimation using a small flash light and a baker's syringe - there's lots of room for improvement, too.

[Shiraz]

wow, that is impressive progress... well done, nice image

The wobble is possibly due to small tracking errors in the mount - what exposure time did you use? The cone+circle shapes are due to coma which becomes progressively worse away from the central sweet spot. Looks like the sweet spot is not quite central in the camera field of view, so collimation is a bit off or the camera is not central in the field of view.

the DIY collimation tool is a good addition to standard collimation techniques because it quickly shows you if anything is way out of alignment - sometimes collimation can proceed even with major misalignment and your system will never really work properly. Don't try to use it as an alternative to standard techniques though - it doesn't tell you everything.

[silv]

cheers shiraz!

my alignment was hm ... quick and dirty? - so I had to make do with 15 seconds ISO1600. 20 seconds were already streaky.

the small tracking errors causing the wobble - like mechanical stops or something? uuuaaaahhhh!
No, no, I don't think that was the cause. On all images the stars all have 1 jitter in them. You know. Like as if you had touched the camera slightly. Such a regular mechanical error would be weird. You'd say so too would you see the jitter. I feel it's the shutter clicking while the camera is in that kind of floating rubber band mount.

Yeah, "coma" - that's the word.

No, I won't be "using" your DIY tool for real collimation. But it definitely showed me that the mirrors are completely off :o


Come on, let's have a beer or some other fizzy drink! :cheers:


:) :) :)

[silv]

this nags at me.

how to find out if it's just the camera shutter or the mount?

if it is the mount, the jiggle should happen multiple times in longer exposures - especially well visible in star trails. (he he he, it's good to be good in inaccurate alignment!)
if it is the shutter the jig will only happen once in any image.

I think I'll do the test again with that rubber band mount.

if it turns out that it is the mount/motor - how would I fix that if not by buying a new mount?
if it is the motor/mount then prime focal photos - even with a proper adapter and focuser - would certainly always show this error? or would the proper focuser and t-connection smoothen the jig - as I hope it would if the shutter were the culprit.

why go prime focal, at all, and invest money in a focuser and t-connection prior to having a proper mount?

yup. next clear night it's another prime focus test. I so hope it's only the shutter...

[Shiraz]

You need to upgrade the focuser and get a camera adapter to make the scope work properly, whatever mount you have. Once you have the scope sorted out it should satisfy your imaging needs for many years to come, so it will not be wasted effort.

Suggest that you do not worry too much about the mount for now - until you get the the scope-camera combo tidied up, you will not be able to easily isolate possible mount problems.

In general though, your EQ5 is a bit lightweight for your scope and it will always have trouble tracking for long periods (although you may be able to make it perform significantly better with a tuneup). However, for now it is a good way to support the scope while you work on it and it will probably be fine for subs up to say 20 seconds - maybe more - if the wind is not blowing. And with a very sensitive camera like yours and an f5 scope, you can image a lot of interesting objects with short subs. Suggest that when you have had fun doing that for a while, you will know what the mount limitations are and you will also know where you want to go next.

[silv]

I hear you, Shiraz.

But I can't just follow your thoughts.
Would I buy a focuser now, I would have to watch out for it's weight and possibly compromise in favor of a lighter focuser. (and pay more or miss out on features that a heavier focuser would have.)

I'll attach the test 30 secs to illustrate why.

Here (http://www.iceinspace.com.au/forum/showthread.php?p=878804#post878804) , someone posted an image taken on a mount close to it's limit (and with properly mounted camera) and it shows the same feature as mine when I take shorter exposures that don't yet trail.

I'll attach also a stacked 8secs ISO 1600 version of NGC3247 - The Whirling Derwish - it's just good to know that DSS can make sense of the broken stars.

[silv]

The 30 secs show 5 bumps instead of only 1.

I noticed that the zoomed live view enables me to do drift alignment (without having to buy a cross hair eye piece).
I will concentrate on that, following Octane's rule of 15. (http://www.iceinspace.com.au/forum/showthread.php?t=73263)
Hopefully that will lead to a better tracking result and I can do another test shot to see whether the mount causes less bumps in 15 seconds exposures when it doesn't have to correct my poor alignment.
If I could even reach 20 seconds I would buy a focuser and go ahead with existing mount. If I can't - then I will buy a better mount straight away.

The EQ5 is said to be able to carry 9kg. (http://stargazerslounge.com/topic/96471-fyi-max-weight-for-eq5heq5eq6-neq6-mounts/) That makes it 4.5kg in the real world. And the added motor already weighs what - 1kg?
omg. I wasn't aware of that.
This package was sold (without the motor) to the former owner (a visual astronomer) and I thought the setup would be working okay if a shop/a manufacturer sells this scope and this mount together.

[Shiraz]

that is horrible tracking. Would have expected a lot better from the EQ5 - looks like there is some irregular friction or gear problem. Could probably be fixed with a tune-up, but you must be confident that you want to do this:
http://www.iceinspace.com.au/forum/archive/index.php/t-17262.html

advice to date has been on getting what you have to work - however, if you are of a mind to upgrade, the question becomes what would be best. To some extent, you are heading down a blind alley with your current gear.

Starting from scratch, an entry level good quality astro imaging system based around your camera would probably be something like:
EQ6 mount (or HEQ5, but only if the EQ6 is too heavy for you)
ED80 scope or similar with field flattener and adapter for your camera
60-70 mm guide scope (or maybe OAG) with QHy5/Orion guide cam

You could decide to sell it as is, but your 8 inch scope would be a good addition to an ED80/EQ6 package - it would be right on the edge of the HEQ5 comfort zone though. You could fit a low cost GSO or Skywatcher focuser - should be OK for your lightweight camera and you will probably need an MPCC as well. If the upgrade to both scope and mount is too much for one step, you could tidy up the 8 inch scope and get a new mount for it.

there would be a market for the EQ5 and 8 inch scope - still fine for visual use.

would be nice to also get the opinions of refractor users on the best upgrade path.

[silv]

cheers shiraz! I wouldn't dare to follow even those detailed instructions at this stage. my DIY skills are rudimentary - uhm, non-existant - I just don't think like a DIY person. (yet)

the previous owner has removed the chinese people's grease.
the mount moves really smooth when operated by hand during balancing.
the motor doesn't make any weird noise. no clicking, either.
he also fitted the GotoStar motor system. and he exchanged the 2ndary vanes with 2 circle ones.
all neat stuff I wouldn't be able to do myself.

I weighed the tube with all gear attached - 9kg.

[Shiraz]

almost all mounts have periodic error due to imperfect mechanical drives - these errors cause wobble in the RA axis tracking and I suspect that is what you are seeing (if so, it is pretty erratic tracking). Your mount probably has errors something like
http://brough-astronomy.webs.com/apps/photos/photo?photoid=141221471 Thus, if you image over 5 minutes, you could produce stars that are smeared to about 50 arc seconds long in the RA direction (and maybe only 4 arc seconds wide). You can do 3 things to improve this:
1. image for short periods - if you image for 10-20 seconds, there will be periods when the RA rate error is small - you can keep these good subs and discard the rest. A photoshop add-in called star rounder can help tidy up slightly elongated stars
2. use PE correction - some mounts can be trained to put in small offsets to the drive to partially compensate for the known errors - don't know if your drive systems supports this and I have no experience with PEC.
3. add a second tracking scope (or alternatively off axis guider (OAG)) with its own camera that can track a star and feed corrections to the mount to compensate for the drive errors. (most people use this sort of system). However, I think your mount drive system will require an additional box to interface with the standard ST4 drive signals used by most tracking systems. Your system is already overweight, so this approach could be tricky.

Suggest an experiment to see how bad the drive system is. do your normal polar align and then deliberately offset the mount azimuth (not altitude) by enough to cause some gentle drift in the declination direction when you track a star near either the west or east horizon. Then do a single 10 minute image with the RA track operating - leave the dec drive fixed - the dec drift will allow you to see what the RA axis does - you should see a sort of sinewave formed by the PE cycle (I think this will work, although I have not tried it).

[silv]

found the "blog" (http://brough-astronomy.webs.com/apps/forums/topics/show/3309026-telescope-mounts-and-associated-errors)related to the periodic error graph you linked.

I feel I might understand the whole thing sometime - but I don't, yet. Can't even ask questions, that's how blurry it all is, for me.

How come, a guiding setup can reduce the mechanical errors? They do still occur: the gears are still too tight or some screws not holding something properly even.
(I'm not going to do auto guiding. Feels like cheating. Wanna do it the puristic way, first. But answering this question above would help me understand a bit more of the underlying problem, I hope.)

Read this thread about tuning (http://www.iceinspace.com.au/forum/showthread.php?t=55025&highlight=hypertune&page=2) a NEQ6. To get a bit of feel for ... something. :o

"leave the dec drive fixed" - how would I do that? Connect the hand controller to the upper motor instead of the lower motor? (I assume they are both "motors" - both boxes have additional ports.)

What is it this 10 min exposure can tell me? A star trail that looks like a sinus curve?

2 of my nightly routines are:
* resetting PEC data in the controller (every setup is different in the alignment quality and if it is recording PE I don't want to use data from a previous setup.) I have no idea what the PEC really does. Apparently, the errors come from the motor wheels not being properly balanced and meshing into each other. How would PEC predict the next mechanical movement error and then how would it work against it? Slow the motor down or speed it up when approaching such a speed bump or a pot hole? (You wrote you don't use PEC. I'm just thinking loud.)

* sometimes using the "sync to target" option when the "select and slew" option has not put the object reasonably well within the FOV of the 40mm eyepiece. I will stop using this function, now, because I read somewhere that some controller software interpret this command as a "1 star alignment" and overwrite the sessions' 3 star alignment.
(Gotostar software is not well documented and outside support, anyway.)

[silv]

I have pondered either buying a lightweight 80mm refractor or buying a new mount.
I can not tell whether my current newt has a parabolic or spherical mirror. (Eden Optics, 8" 1000mm f/5) There is no info anywhere on the internet. If it has a spherical mirror, the expense for a new refractor could be justified, regardless.
I can not tell whether the EQ5 has such severe problems that will be inherited by a lighter scope, too. I know, you wrote, the EQ5 will cope well with a scope half the weight. But I feel insecure, here. Not really understanding what the problem is - and risking that the expense for a new refractor will leave me moneyless when it turns out the mount is simply not good enough for even non-artistic, pure discovery AP like I want to do.

I bought a GSO crayford focuser and am awaiting the t-minus adapter.
I doubt the focuser will dampen the bumps. But I will give it a try, anyway.
I will also see what happens with tracking stars close to the eastern, northern horizon (I don't have a southern or western horizon due to forest) or high up at the zenith.
And I will try and have more weight at the east for every different object as I read that this might help the motor, too. (I didn't understand the reason, though.)

It's likely that the tracking errors are insufferable for me.

I made a brave decision: I will take the mount apart. :o

I am currently looking for a new profession and was actually considering going into something more to do with my hands. Life is short and I've never worked with my hands, before. Would be a shame not to try that before I die.
Instead of making a profession of it (weird, how I still regard my jobs as my prime source for passion, fun and fascination) - and who would train a 45 yr old female, anyway - I could realize it with this project. Will be tough I reckon. I only have my small bed room. Only the desk can hold all the parts while I'm working on them for quite a while. And doing it without any guidance and knowledge - nor understanding yet all the English terms (e.g. what's a "worm gear"...) is an ... adventure.
But taking this diversion from the straight path has its merits for me, personally. Letting go of the desired goal "AP" for a while and embracing the opportunity at hand. It's also a spiritual practice, probably bringing my soul closer to Nirvana ;)

ZeroID, in case you read this: I would not want to occupy your work room, in case you are about to renew your offer. :)
I understand it will be a project that will take a few long sessions, possibly even including wait time for spare parts. I want to be able to work on it whenever possible and not feel I might become a nuisance to you.

[Shiraz]

Mechanical errors arise because it is just not possible to make gears etc with the extreme accuracy required for near perfect tracking. The gear and bearing tolerances need to be maybe 1/100 the width of a human hair to get fine tracking and no readily affordable system is that good. Guiding with a second scope overcomes the effects of the mechanical errors (which are unavoidable) by adjusting the tracking speed to compensate for any drift in a star being imaged by the guide scope - eg if the star being guided on moves ahead on the guide scope camera, the guide software effectively tells the mount to slow down a bit - and vice versa. In a perfect system, if the star can be made to stay in the same place in the guide scope, the images taken by the main scope will stay as points as well. The mount still needs to track smoothly though for this to work properly and EQ5s are pretty jerky. Even the $10k+ crowd use guiding to tidy up mount tracking inaccuracies.

When doing the suggested 10 minute test, just set the mount tracking normally and don't touch the Dec or RA adjustment buttons. For a 10 minute long exposure, I guess you use the bulb setting on the camera and leave the shutter open for 10 minutes. The test will show you how rough the tracking is. It is pretty hard to assess just what your mount is doing without some form of test results that we can measure.

If you have no idea what PEC really does, then turn it off if your mount software will let you. PEC has the potential to mess things up if not done right and you might improve the mount by disabling it. Only use it when you understand it. What process do you go through to train PEC at present?

Don't know the brand, but I would be surprised if your scope has a spherical mirror - maybe the original owner could help. When you have installed the focuser, I would hope that you will have a pretty good scope.

It is a really brave decision to dis-assemble your mount if you are not confident, especially if someone else has already cleaned it up. Your call, but suggest that before you do a full pull down, you work out how to adjust the RA and Dec worm clearances to minimise slop in that part of the gear-train. This could possibly improve your mount by quite a bit without too much risk and there are video tutorials that should help you. EDIT: just found this in your other thread - you should definitely adjust the worm gears. whereas before, pushing the left-right-up-down buttons almost immediately reacted and moved the scope into that direction,
tonight, the scope first performed a tiny backwards circle before it then "found" the direction it should move to.

My overall advice is still to get the scope and camera working OK and then start on the mount. Then get the mount working as well as possible and do some unguided imaging with short exposure subs. Getting good results from imperfect components can be a satisfying art form in its own right. Once you have done enough imaging to know what the true capabilities and limitations of the mount and the scope are, you will have a fair idea of where you want to go next - and that will almost certainly include a better mount. have a look through the show and tell forum - lots of scopes that look a bit like yours, but on heavier mounts. eg http://www.iceinspace.com.au/forum/attachment_browse.php?a=66197

since this thread is becoming more about the mount, suggest that it might be a good time to start up an EQ5 performance thread and tap into the knowledge of those who have used that system.

[Screwdriverone]

Hey Silv,

What sort of 8" newt do you have?

I solved my in-focus issues by buying one of these for my Skywatcher 8" F5 newt, I still have about 12mm of inward focus travel with this baby in. I tried the mirror springs and screws and the slop in the primary (it leant over) was so bad the coma was horrible.

Works for me, not sure if you have a Skywatcher or not.

http://modernastronomy.com/accessories.html Scroll down to 2" Adapter with Compression Ring - for SkyWatcher Newtonians with M54 thread.

Hope this helps (or at least shows you how to solve the problem on your scope)

Cheers

Chris

[ZeroID]

Silv, good on you for wanting to get stuck into the project but I suspect you might be biting off a bit more than you think pulling it all to bits if you don't have a good idea as to what you are looking for.
You might do better getting some help in your setup to see what else is going on. Balance, alignment and loading may be a large part of your problems at present that someone would be able to point out without stripping and rebuilding unnecessarily.
I'd suggest going along to one of the Auckland Observatories evening sessions and having a chat to someone there. Hopefully they can show you some solutions.
I don't think Nirvana is found pulling mounts apart.
I have quite a large garage btw so a bit of space would not have been a problem.