Lordspace

If I use a 18-55m lens on my 450d with a aps-c sensor on 55mm the the focal length or crop factor would actually be 82.5m so the same would happen with a telescope as it's just a lens?? 

If I attached my canon to the telescope the focal length or crop factor would be 1875mm 

So what would it be for a 1/3 size sensor??

Surly it would increase the magnification?? 

Hi, my (webcam) astro camera has a sensor of 1/3 and my telescope focal length is 1250mm what would the focal length be when then image sensor replaces the eye piece?

I know that canon aps-c is times by 1.5 or 1.6 what is the math for the 1/3 sensor.

Cheers

1 hour ago, Waldemar said:

https://www.bing.com/images/search?view=detailV2&id=1E502F26DB74498AD81488DF53D9F9FC3E22F190&thid=OIP.5sZqFlIJJVT6PjL1RVSrSQHaFL&mediaurl=http%3A%2F%2Fensoptical.co.uk%2Fimage%2Fcache%2Fdata%2Fproduct-3179%2Fcounter-weight-a2-1000x700.jpg&exph=700&expw=1000&q=balance+system+for+etx+90&selectedindex=42&ajaxhist=0&vt=0&eim=0,1,3,4,6,8,10

I made my own with a bit of old wood and an old metal tripod top, as astronomy manufacturers like to try and rip us off. No way is a couple of weight and a bit of metal worth £200.

They must think we are crazy.

26 minutes ago, Waldemar said:

Balancing is very critical, not only for imaging, also for visual, albeit less. 
So... to prevent your mount from giving up on you, please pay attention to the balance!!

I just assumed it wasn't as important on fork mounts as stole can't be moved forward or backwards like a scope on a GEM mount. 

I will try and pay attention next time I take the scope out.

Yeah, couldn't remember what it was called.

I use the scope as is tbh without balancing didn't think it would make a difference unless I ran it with a camera.

I only asked as I noticed it wouldn't lift the scope yesterday it would get half way and stop but the gears were still moving so thought maybe there wasn't enough friction on the clutch.

This is the clamp, but the gear and plastic gets pushed together when doing up the Dec setting circle but I'm not sure if it is meant to have a rubber ring to help with friction. 

27 minutes ago, Waldemar said:

Maybe you can attach a picture, to be sure?

If you mean the dovetail on the scope and the dovetail clamp on the mount, then no, there should NOT be any rubber things in between.
The clamp should grab the dovetail in a solid way, without any possible movement.

 

Its hard to show as I would have to remove the scope and undo the Dec clamp. Basically there is a clamp on the side that has to be done up so the motors can engage but as this is just a friction lock it isn't very strong, I've seen one post with a picture showing a runner spacer to help with grip but I'm not sure if they added this or if it's stock.

Mine does not have one and the plastic and metal gear won't have much friction.

Just a quick question for anyone in the know, 

On the Meade etx 90 Dec clamp should there be a rubber ring to help with friction when clamping down the Dec knob??

If there should be one then I obviously have somehow lost mine as even when I clamp the Dec knob all the way down I can still move the scope up and down so it can't be getting enough friction.

Cheers

15 hours ago, PEMS said:

It is very likely going to be difficult with a Meade ETX 90.

There is no polar scope on them so any polar alignment will be approximate. Using the scope itself is not correct and invalid. Then the scope is a long focal length so what errors present gets in a way amplified and the scopes is therefore slow.

You have I suppose very little that makes your life easy for gathering images.

If using a wedge have you a Wixey for setting the angle correct and I know of little equipment that will align the mount - note, not the scope - to the NCP.

I will be using a filed reducer to make it closer to 600 focal length.

I have been looking at maybe going the drift align method to clean up what inconstancy is in the align process but as I don't have an illuminated reticle could I use my imaging camera and the capture software as the reticle?

4 minutes ago, Space Bat said:

Polar alignments can be a daunting task.. it takes practice!  If you persevere eventually you will be aligned in minutes. 

You can get pole scopes for forks btw

I didn't know you could get them, I will have to take a look.

My mount likes to make polar alignment difficult as when it spins and does it's thing to polar align some times the eyepiece is pointing to the floor so it's very awkward seeing if Polaris is in view.

Is astro photography worth it when not using auto guiding?

No matter how much attention I pay to alignment it seems I am always limited to 30 seconds. 

Is this just want I will have to live with as my mount isn't capable of guiding...

Well I don't think it is anyway.

I also understand my mount and scope isn't meant to such a task as it's a fork mounted scope.

But is there anything other than spending hours on polar alignment I can do?

I have a Meade etx 90 with a reducer.

I think my mounts issue was not down to any particular grease but the light diode or whatever it is called. 

The is a clear part then the gear with teeth spaced apart and a blue part on the other side...

Well the blue part had been tilted back away from the gear so I pushed it back towards the gear and the strange slew problems seem to have gone. So hopefully the grease will work fine and the mount will be usable again.

17 minutes ago, Geoff Lister said:

I know it is counter-intuitive, but would the (old) thicker grease help dampen-out any resonances in the gear train?

So far I've read a few articles online that said the same thing.

I'm wondering now as white lithium grease is very light that is may not be binding the gears enough to help with the right amount of bite.

To me the grease looked old and sticky but it seems it was meant to be like that.

I'm more worried about the erratic stuttering the gears make when slewing at slower speed.

It wasn't making noise like this until I had to replace a gear. And now both RA and Dec are giving erratic behaviour Inthe gears but they work fine at make slew speed. 

Its very strange. 

I left the cover off to show how the gears would jump and stutter at slow speeds.

I have added a link o a video of how my mount now sounds after changed only grease and a single plastic gear.

Both the RA and now Dec are having slewing issues.

I'm sure or I hope you can hear how bad the mount sounds when slewing.

The Dec gears only had new grease which I'm sure should cause an issues like this.

If you have been following my troubles with this hobby then you will know I had to replace a gear in my etx 90 mount.

While I was in there I decided to clean of all the sticky grease from both axis,

I used lithium grease as the new grease but not both axis stutter and malfunction in every speed but Maximum.

Will the grease have a negative affect on the gears?? 

If anyone can recommend better grease or if it's better to just not use any.

(Nothing but trouble so far and only been back in the hobby a few weeks)

Cheers

After an hour of cutting and sanding the we fits perfectly fine now and the mount works with no issues so far.

Just got to retrain the motors and calibrate and give it a real test.

But thanks for all the help and advice..

I would have just sold the mount if it had not been for all the help on here so I really do appreciate it!!!

On 26/02/2020 at 19:46, KevS said:

 

Well I got the gear from accu this morning.

The general size seems fine in diameter but the sticking out part is huge so hopefully it will fit.

If not someone has offered £25 for the mount as spares.

If it doesn't work hopefully they will let me return it.

1 minute ago, KevS said:

May I interject? 

You will probably find that the external diameter was originally 12.54 mm (Meade being an American company) 1/2 inch in old money, the bore being 3.2 mm 1/8 inch. Try a search for "imperial gears". Might find the exact one that you are after. 

That makes sense, I will have a look see what I can find.

Its amazing how it can be so difficult trying to find a small round piece of plastic with teeth.

Well I went for the brass one on that site £12 all together so I hope it works haha

13 minutes ago, MarkAR said:

Excellent, so a PCD of 12mm, 24 tooth, 3mm bore in delrin is I believe what you need. Accu.co.uk only do that one in brass or steel. Brass might be ok.

PCD is the diameter measured from half the tooth height.

AHH ok, I think I saw the brass one. Would brass be ok next to plastic gears? 

4 minutes ago, MarkAR said:

I think thats a pretty standard part, measure across the diameter with a rule and also the hole. The hole will only be either 3, 4 or 5mm.

The teeth look like 0.5 MOD, so I'm guessing that the diameter is 13mm.

The closest spurr gears that Accu comes up with is a 0.5 MOD, 24 tooth, 12mm PCD, 3 and 4mm bore.

 

My calipers show the diameter as 12.5 but I'm sure the 0.5 wouldn't matter would it. The hole is 3mm and there are indeed 24 teeth. When ever I search on any sites I always find close to the one I need but never exactly.

I am looking for someone who can 3D print me a gear for my Meade ext 90 RA drive.

I am willing to post the broken part out at my cost to you, so hopefully someone can copy it and then send me a couple.

I am willing to pay for the service.

Cheers

1 minute ago, joe aguiar said:

no its not that bad at all

just the hand controller autostar alone  last time I looked almost $150 with tax u can get $90 to $99

then someone like u that had another part break can or will buy your to use the part he needs maybe $40 to $50 if that part wasn't broken you would get a lot more.

If I sell my etx 125 base fork arms and hand controller I would list it for $199  yes your is broken so it get a lot less

A eq2 can handle the 90mm mak, its not a write off the ota is an excellent little scope.

a eq2 used can be $60 in uk maybe that's $35 not expensive at all

joejaguar

I only use goto mounts tbh or tracking mount as i used the mount/scope for imaging... I'm not really into just viewing so kind of useless to me now. 

I can't see why Meade wouldn't sell spare parts when they still sell the mount/scope.

I was quoted £65 for the whole gear set from a third party vendor which is was too much just to fix this mount.

The value of the mount would be next to nothing now it doesn't work.

I wouldn't get any where near enough to fund a new mount 😕 I have no idea how to even calculate the dimensions for a new gear and I doubt I could just get one from eBay.

Looks like I may just have to sell everything as faulty and cut my losses...