I'm planning to bootload a Atmega8A smd version with Arduino Uno R3 as ISP using IDE version 1.6.12 and Arduino NG as board/Atmega8.
Can someone tell me how to use the internal 8Mhz if I'm not wrong oscilator instead adding capacitors and a outside crystal.
And does the ATmega8A smd version supported by the IDE bootload ?
D.60
You don't wanna use the "Arduino NG or older" option, as the bootloader is occupying 1/8th of the flash memory, is slow to start up (originally made for manual reset before upload), and is not built for an 8 MHz clock.
You're also going to run into a bug that where introduced in Arduino IDE 1.6.0, because the ATmega8 doesn't have an external fuse, like its younger brothers got. Long story short; you should probably just go with MiniCore, which takes care of all these problems. If you do a manual install, you'll get independent BOD settings for the ATmega8, as I haven't released the latest version to the boards manager installer.
Looks like a lot of work for me, I'll better buy a atmega328 smd, bootload it with arduino IDE and uno as ISP and buy as well a smd 16Mhz crystal.
Domino60:
Looks like a lot of work for me, I'll better buy a atmega328 smd, bootload it with arduino IDE and uno as ISP and buy as well a smd 16Mhz crystal.
Long story short; you should probably just go with MiniCore, which takes care of all these problems. If you do a manual install, you'll get independent BOD settings for the ATmega8, as I haven't released the latest version to the boards manager installer.
No, it's not 
Solder your SMD ATmega8 to a board or something. Download MiniCore. Choose the prefered clock frequency. Choose your prefered BOD option. hit "Burn Bootloader". It's that simple
- There might be some issues related to the internal oscillator. It's factory calibrated, but may be a little "off" depending on the calibration, ambient temperature and operating voltage. If uploading failes while using the 8 MHz internal oscillator
Not sure but I don't trust something that may not fully functioning.
It's true that the internal oscillator may be a little off depending on the factory calibration and ambient temperature. If strict timing is required (e.g asynchronous serial) an external oscillator is reccomended, either you're working with the ATmega8 or the ATmega328. My conclution is: you shouldn't dismiss the ATmega8, just because the Arduino guys aren't selling the hardware anymore. The Arduino core files are up to date and runs perfectly on the ATmega8
So what is the recommended crystal for the atmega8A and am I able to use directly the arduino IDE
to burn the bootload ?
These are your oscillator options:
16 MHz is standard for most Arduinos, so you can't go wrong with that one. 12 and 8 MHz also works fine
If strict timing is required (e.g asynchronous serial) an external oscillator is reccomended,
Well yes I'm trying to make a watch 
so looks like even if I tried to skip the external crystal I need to
add one to have precision oscilations.
Wait, in that case that I use 16Mhz in my case crystal, am I now able to bootload directly from the IDE
that I have? and what board should I use?
If you're going to make a watch, you'll have to go for a real time clock like the DS1307 or the DS3231. Even if an external oscillator like the 16 MHz one is really accurate, the micro controller itself isn't accurate down to ~seconds per month. A pure micro controller based watch will work, yes, but what about a week later? Or a month? Stick to an RTC, that what watches does
But wait crystals are used from old times to watches and they are used till nowadays to out wall watches
why wouldn't a crystal as 16Mhz not being able to keep a constant and accurate time?
btw about the IDE and bootload what board to use to upload the bootloader to atmega8A with 16Mhz?