Motion of telescope on a wedge

[Space Manta Ray]

I'm having a hard time visualizing the motion of a telescope (celestron 8SE) on a wedge as it follows an object from North to South.  Does anyone know of a video available that I can watch this?  I'm wondering if my DSLR on a Celestron Deluxe tele-extender will bottom out on the base as the scope travels from the NE horizon to the SW horizon.  I am located at around 45N.

[Demonperformer]

I know this is not the question you asked (and I just hate it when people do that with questions I ask), but if you are thinking of buying one of these, I wouldn't. You will be much better off investing in an EQ mount for the scope. Yes, it will be more expensive, but it will also be much easier to use and the result more stable.

[Merlin66]

If the OTA with the extender and camera fit between the rear cell and the base of the forks then you’ll be OK.

 

[barkis]

As Merlin has just said, you can manually move the OTA through the fork with the configuration you wish to use.
Slowly move it around noting how much clearance there is passing through the Base. If all is well, you are good to go.
I've heard too, that wedge mounts are not particularly good when it comes to guiding long exposures.
You can be your own judge on that issue when you have tried it yourself.
I've seen some very fine results on deep sky targets from wedge mounted telescopes.
Good Luck with yours..

[Cosmic Geoff]

I advise you not to spend your money on a wedge for the C8 SE.  I assume you have deep-space astrophotography in mind, since an equatorial mount is not essential for planetary astrophotography.  While the C8 SE is great for visual, its deficiencies for planetary astrophotography soon become apparent. The drift, vibration and backlash effects are largely covered up by  stacking software, but I anticipate that if you buy a wedge and try deep-space astrophotography you will soon be wishing you'd spent your money on a different setup.   The recommended telescope/ mount setups for deep-space astrophotography are well known, and the  SE mount does not figure in them.

[MartinB]

When I was deep sky imaging with a Celestron NS8 the scope couldn't point straight up because there wasn't sufficient clearance.  This meant some circum polar targets were off limits.  This restriction aside, I had no problem imaging with a Good quality wedge.  My first wedge was a Celestron "heavy duty" model which was very poorly engineered and nigh on impossible to polar align.  I upgraded to a better wedge which transformed things.  There is nothing inherently wrong with using a wedge.

The position of the scope doesn't change in relationship to the forks as it tracks across from NE to SW.  One bonus of a wedge is that you don't need to perform a meridian flip!

[Louis D]

There's nothing inherently bad about wedge mounted SCTs.  The older SCTs from the 70s/80s/90s used well machined drives similar to GEMs and had very smooth tracking with low PE.  The move to sloppy, lower cost goto mounts with stepper motors changed all that.

[Davey-T]

I've been imaging with my wedge mounted SCT in the Cassiopeia region recently, around the +60 degrees region, pretty much scope straight up but wedge forks at an angle so camera doesn't go between them.

As said, once the scope is at the right dec' angle it won't alter during tracking.

Dave

[Merlin66]

I successfully used a Meade 12”  LX 200 on a reworked HD wedge and tripod for spectroscopy for many years. Proper balance was the key.

only sold and replaced by the C11/ NEQ6 due to the fork restrictions with the larger spectroscope.

[michael8554]

The Celestron deluxe Tele Extender allows you to do high magnification eyepiece projection imaging, which I assume means you want to do planetary imaging.

In that case the mount should track a planet for short video sequences without a wedge.

If however you are considering Deep Space Objects, the single fork 8SE isn't robust enough for serious long exposure imaging IMO.

Also you would probably not need the eyepiece projection, more likely the other way with magnification ie a Reducer.

Michael 

[Demonperformer]

I think a key point to remember is that OP has stated he has an 8SE. Having owned both a 6SE and an 8SE, I would say that the mount is barely capable of AP, with the exception of SS, and that is when the centre of gravity is firmly over the tripod. A wedge moves that centre of gravity to one side and that is bound to make the entire setup less stable. If OP were planning on making a wedge, at little cost, it might be worth a try, but these wedges are quite expensive. OK, not as much as would be needed for a suitable EQ mount, but I still say that this £300 would be better put towards a decent EQ mount.

Other mounts may work well with wedges, but this one would not - certainly not for long exposures - and if you are only taking short exposures (and I have taken some deep sky images with this scope using 5s exposures with a cmos camera) just use AZ and crop the final image.

[Space Manta Ray]

Thank you all for the very informative replies.  I will take these all into consideration.  At the present time, I am not able to afford an EQ mount, unless someone feels obliged to make it possible for me to acquire one really, really, really cheap.  Until then I will be looking at one of the other options mentioned.  And, I have to still build my observatory in the back yard and run cables to the basement office.

Clear skies (what is that?) to everyone.

 

[Davey-T]

35 minutes ago, Space Manta Ray said:

And, I have to still build my observatory in the back yard and run cables to the basement office.

If you're into DIY and you're staying at the same location it's easy enough to build your own wedge out of something like 3/4" plywood.

Dave

[Geoff Lister]

On ‎17‎/‎10‎/‎2018 at 02:21, Space Manta Ray said:

I am located at around 45N.

I am located at about 51.4N, and have been experimenting with mounting my Virtuoso 90P (lightweight Mak. on a Dob. mount) on a wedge made from chipboard. It is clear that, by using a wedge at 38.6 degrees, the centre of gravity is thrown well forwards of the azimuth shaft, and puts an asymmetrical load on the plastic slip pads near the circumference of the base. If you are at 45N, the wedge angle would be 45 degrees, making any load even more unbalanced.

Geoff 

[Davey-T]

1 hour ago, Geoff Lister said:

I am located at about 51.4N, and have been experimenting with mounting my Virtuoso 90P (lightweight Mak. on a Dob. mount) on a wedge made from chipboard. It is clear that, by using a wedge at 38.6 degrees, the centre of gravity is thrown well forwards of the azimuth shaft, and puts an asymmetrical load on the plastic slip pads near the circumference of the base. If you are at 45N, the wedge angle would be 45 degrees, making any load even more unbalanced.

Geoff 

OP is using an SCT.

Never had a lot of luck imaging with wedge on a tripod but it works fine on a permanent pier.

If you're making your own you can make the base bigger to offset it from the tripod for better weight distribution.

Dave

[Geoff Lister]

10 hours ago, Davey-T said:

If you're making your own you can make the base bigger to offset it from the tripod for better weight distribution.

I did just that. As the Virtuoso mount is a table-top Az/Alt Dobsonian, I made an extended base for the wedge and added 3 small feet. I also determined the average balance point of the whole assembly and made a short screw-on adaptor, so that I could mount it on the tripod from my Skymax, and with the average balance point over the centre of the tripod.

The instruction manual that came with my Virtuoso, has a section on attaching the mount to a tripod-mounted wedge, and, with a button-pressing sequence at power-up, the mount should go from Az/Alt to EQ mode. The manual now on the Skywatcher website does not have this information, and I could not "persuade" my mount to go into EQ mode. So, I re-calibrated the mount for Az/Alt operation at the North Pole (where Az/Alt and the EQ's RA & Dec are the same), attached it to the wedge, and powered-up as for normal Az/Alt operation. This gave me Az = RA sidereal tracking and an essentially zero Alt movement. I have yet to try it for imaging.

Geoff