Experience of AP with an EQ3 Mount

[Stub Mandrel]

I'm considering upgrading from my EQ3, so prompted by another thread, I thought it might be a good idea to summarise some of my experiences of using an EQ3 mount.

Despite the book MEPC setting the EQ3 as the 'minimum standard' for AP (to the chagrin of alt-az imagers), it is often dismissed out of hand as an AP mount.

I started off using my bridge camera, but got my EQ3 in spring 2015 along with a 150PL, and spent the summer getting increasingly creditable planetary images.

By the winter, I got a second-hand Canon 10D and fitted a home made RA drive. I added a number of tweaks to stiffen up the tripod and though at first PA was rather hit and miss, I got some of the well known objects, and then ended up getting an EQ5 tripod and astro-modding the 10D. This image was using the 150PL, unguided and shows the EQ3 is not a write-off:

I could get reliable subs of 30s to a minute with a high success rate.

Further work saw me add homebrew DEC drive and goto to the mount and I rapidly upgraded to a 450D, which I also modded, and then to a 130P-DS. In summer 2017 I modded the 130P-DS to add cooling and the desire for longer exposures meant taking on guiding.

I made my own guidescope with 163mm focal length by modifying a cheap 300mm scope with a new lens doublet. I do wonder if I should have left it at 300mm. I use an ASI120MC as a guide camera and it always finds stars. My homebrew box uses ST4 only. The precision of my driver is 0.87"in RA and 0.67" in dec, the 130P-DS and 450D gives 1.83" per pixel.

I understand the EQ3 Synscan can do at least as well as this.

Jumping straight in with cooling, Ha and guiding for the first time on the same night was over optimistic! I have been dogged by large swings in DEC caused by a combination of backlash and stick-slip. I did a fair amount of fine tuning, including adding roller bearings to make the DEC axis less 'sticky'.

Gradually I discovered that a combination of good polar alignment, good DEC adjustment could give greater reliability. This is a PHD2 log from a good night, the overall RMS error is about 1.4".

Sometimes guiding is good at about 0.80"RMS, but often spoilt by sudden big swings. I have managed a few long runs at this accuracy, but the log files appear to be too big for the viewer!

Here are a couple of relatively recent images, the first is Ha:

 

My conclusions are:

1. The EQ3 mount is perfectly suitable for beginners in astrophotography
2. The aluminium tripods are not ideal, but a 1.25" steel tripod will give much improved stability.
3. It is worth stripping and greasing the EQ3 (I used teflon grease) and being prepared to re-tune it in DEC every few sessions.
4. With good polar alignment (I use the 'new reticle' polarscope) you can achieve a reasonable level of successful subs up to 1 minute at 1200mm end even up to 2 minutes at 600mm.
5. With guiding 600+ second subs give a very high level of retention, unless the DEC axis is in poor adjustment.

 

 

[wimvb]

Good write up. What is missing is of course an image of the mount after all your adjustments and addons.

[Stub Mandrel]

Some pics!

Roller bearings at each end of DEC axis

RA drive

You can see RA and DEC drive in this one with a Jessop's 70mm scope rescued from a mate's skip and refurbed

Goto box

 

[wimvb]

Neat! You kept the original Alt bolts, I see. Those were the first to go for my EQ3.

Did those roller bearings improve the behaviour much? I always found my EQ3 difficult to balance.

[Stub Mandrel]

3 hours ago, wimvb said:

Neat! You kept the original Alt bolts, I see.

Better design than the HEQ5! The 'flag' bolts clash with the body of the mount at high latitudes.

No trouble with balancing, in fact I always kept it a bit out of balance.